Can't turn on my pc

Hello,

Maybe the title's question is stupid...I have this problem:

When I try to start my pc the hdd light flashes for a half second and nothing else. If I press again the start button it doesn't do anything, but if I hold the start button for a while (like tha manual turnoff) then I can try another time, but with the same result, till 20-30 intents then (if it wants) it turns on. Afer that, it seems everything works okay (no fan problems, no energy problems)...

Does anyone have the same problem??
I'd like to solve the problem by myself I mean without having to carry the pc to the store (I'm afraid they'd say "mmmm... big trouble...you should buy a new one")
Can you help me? Any idea?

Thank's in advance
Niara

Looks like a problem with the power supply unit, perhaps? Maybe it needs replacing.
The answer in any case cannot be buy a new computer. As you noticed, it works. Besides unless you put it under a press, computer problems are usually dealt with by replacing damaged parts. Not the entire thing.

Ok Mario F. thanks for the help and your time

Maybe that's all I have to do, I will check it out.

Niara

It could also be that your power supply isn't strong enough for all your hardware. A while back I put some new hardware in my old PC and when I tried starting it, it would start for a second or two and then shut down. I put in a bigger power supply and it worked.

Definitely a PSU issue. Either not enough power or it's a bad PSU. You could also have a direct short in one of your power cables (I would suspect the 4 pin power connectors) which is tripping the breaker in the PSU.

Another similar problem I have had is in the switch itself (the connecting wires were loose), so it would occasionally turn itself off, or be impossible to turn on. All I had to do was open the front panel and do a little crude soldering.

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Originally Posted by MK27

Another similar problem I have had is in the switch itself (the connecting wires were loose), so it would occasionally turn itself off, or be impossible to turn on. All I had to do was open the front panel and do a little crude soldering.

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I've never look inside a power supply, but I'm guessing it has some pretty big capacitors in it, so I would avoid tinkering around in there unless I had the right kind of safety equipment (like thick rubber gloves). :)

Your power supply is overloaded. Either take some unneeded peripherals out of the system, or get a larger power supply. Technically it could also be too large, but thats generally not the case unless you are using an industrial PSU.

Hey lots of comments, thank's all for that, and sorry for the delay on response.

I'll try to change the PS for an old one (from an old pc I have in a corner); if not I'll buy a new one.

Thank's
Niara

A last comment, if someone else has in the same problem: for the moment (while I'm waiting for the inspiration to change the PSU) I have unplugged one of the 2 cd/dvd drives and now it works. I know that's not a good solution, but for the moment...

Thank's
Niara

You could also underclock your cpu and/or gpu. Both are power monsters.
I've had to underclock my gpu to play any games since the PSU can't feed it at full power.

lol, I remember when this repeativly happened for a new PC I bought xP In the end I got my money back ;)

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Originally Posted by cpjust

I've never look inside a power supply, but I'm guessing it has some pretty big capacitors in it, so I would avoid tinkering around in there unless I had the right kind of safety equipment (like thick rubber gloves). :)

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:p No, I meant the dippy little plastic front panel switch, not the power supply switch. If it was the power supply switch, I'd have just replaced the power supply. I think this is one of the half dozen times I've touched a soldering iron since high school shop. Don't open the power supply kids!

Obviously this is not the problem here tho, but boy was I relieved when the thing kept shutting off, then wouldn't turn on, then it turned out to be the first thing I checked and took about 5 minutes to fix. Like dodging a bullet or something.

Right, at the end I bought a new psu and all work's all right. The only problem is that the old psu have the fan in a side, and the new psu has the fan in another side (I forgot to check that in the shop), so I'm not able to fix it in the psu place without set the fan inside the case; for the moment I've left outside.

Ah MK27, I have opened the old ps (breaking all the warranty precints), just to see what's inside (unplugged, of course).

And that's all, thanks for your help; for my part the question is finished, and I hope that can be a help for someone else.

Niara

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Originally Posted by Niara

Ah MK27, I have opened the old ps (breaking all the warranty precints), just to see what's inside (unplugged, of course).

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Unplugged or not, capacitors continue to hold an electrical charge long after the power has been cut off and can be deadly. My electronics teacher said a friend of his touched a screw driver to a big capacitor in a large speaker/amplifier one time... The guy was thrown across the room and the end of the screw driver was melted.

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My electronics teacher said a friend of his touched a screw driver to a big capacitor in a large speaker/amplifier one time... The guy was thrown across the room and the end of the screw driver was melted.

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Was it a capacitor the size of a water tower?

I would imagine it takes a lot of energy to melt the end of the screw driver and throw a guy across the room (heat makes gas rapidly expand?). Capacitors don't store a lot of energy. They just can discharge very quickly. Their energy density is a few orders of magnitude smaller than that of batteries.

The current they store is pretty small, but the voltage they can discharge is really high.
Feel free to prove my teacher wrong, but I'll just take his word for it. ;)

Reminds me of when I touched a open wire from a freezer, I just stood there shaking for a little while, like in movies and such xP But I have to say it was refreshing, most likely 'cause it gave me adrenaline ;)

Well, current would depend on the equivalent impedance (resistance) of the load, and is really not up to the capacitor :D.

It will just discharge faster, and the voltage will drop faster, if the current is higher (if you have infinite resistance, aka open circuit, and an ideal capacitor, it won't discharge at all), since for a capacitor, q = CV (where C is the capacitance, and q is charge stored), and delta_q = I*t. The total delivered energy will be the same (that's the conservation of energy).

I haven't done anything with electronics since high school, so whatever you want to call it... The amount of electrons stored in the capacitor, or whatever.

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Originally Posted by cyberfish

current would depend on the equivalent impedance (resistance) of the load, and is really not up to the capacitor

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Apparently, one of the teachers in a school of mine once said to a class of both boys and girls: "when the charged capacitor is all alone with the resistor, it cannot resist the temptation to discharge into it".

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Originally Posted by cpjust

The current they store is pretty small, but the voltage they can discharge is really high.
Feel free to prove my teacher wrong, but I'll just take his word for it. ;)

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Assuming a 75 Kg individual, beign thrown 3 meters in lets say 3 seconds, nto realy thrown, mroe liek pushed, but for arguments sake. That woudl require 75,000 Joules of energy. Since a Coulomb can store more or less 1 Joule, that means you would need 75k coulombs of charge. Lets say the PSU was in Europe and was charged to full line peak voltage of 312 V. That means you would need a 240 Farad capacitor. Since the capacitors in a power supply are electrolytic, and rarely even approach 1 farad, that means your hypothetical capacitor would be at least 240 times the size of a normal power supply unit. Also remember that this is assuming 100% efficient transfer and conversion of the stored energy into kinetic momentum in the individual being thrown.

Your teacher exaggerated his facts, but is correct in telling you a story that will scare you into not doing something stupid like sticking a screw driver into a PSU to see what would happen.

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Originally Posted by abachler

Assuming a 75 Kg individual, beign thrown 3 meters in lets say 3 seconds, nto realy thrown, mroe liek pushed, but for arguments sake. That woudl require 75,000 Joules of energy. Since a Coulomb can store more or less 1 Joule, that means you would need 75k coulombs of charge. Lets say the PSU was in Europe and was charged to full line peak voltage of 312 V. That means you would need a 240 Farad capacitor. Since the capacitors in a power supply are electrolytic, and rarely even approach 1 farad, that means your hypothetical capacitor would be at least 240 times the size of a normal power supply unit. Also remember that this is assuming 100% efficient transfer and conversion of the stored energy into kinetic momentum in the individual being thrown.

Your teacher exaggerated his facts, but is correct in telling you a story that will scare you into not doing something stupid like sticking a screw driver into a PSU to see what would happen.

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When people say they were thrown by electricity, it isn't the electricity itself that throws you, it's your own muscles that react to the electrical shock that throws you. :rolleyes:

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Originally Posted by cpjust

When people say they were thrown by electricity, it isn't the electricity itself that throws you, it's your own muscles that react to the electrical shock that throws you. :rolleyes:

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No no, it means you stand shaking for awhile and smoke comes from your hair, then you get sent across the room and into a bar or something that would 'cause extra damage... Maybe also light a fire that interacts with some gas or fuel and then have a massive explosion... That's what Hollywood told me.

The screw driver is a lower resistance path. Why would the current want to go through you?

Even if it did, assuming the hand is 2 cm away from the conducting core of the screw driver (shortest air path), and air has a dielectric strength of ~2MV/m, the capacitor will need to be charged to about 40000V to cause a dielectric breakdown (air partially ionizes and starts conducting, like in lightning).

And to melt, let's say, 1ml (8g) of steel, which has a heat capacity of ~500 J/kgK, heat of fusion of 247J/g, and melting point of 1500 degrees C. One would need

(1500-20)*0.5*8 + 247*8 = 7896J. That is a lot of energy (the maximum power your outlet can put out without blowing the fuse, for 5 seconds).

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Originally Posted by wikipedia

Conventional electrostatic capacitors provide less than 360 joules per kilogram of energy density, while capacitors using developing technologies can provide more than 2.52 kilojoules per kilogram

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This sounds like a job for Myth Busters.