well i have the same motherboard and a similar cpu on another computer so i might just swap them next time i have them in the same house and see if the problem is the motherboard/cpu or something else by process of elimination
thing that sux is that sometimes it workes for a week or so, so it could take a while to figure this out
Some motherboards have temperature sensors on them for the video card. When the video card heats up the mobo cannot accurately control the temperature of it and so this sensor can cause the system to reboot and/or shutdown.
Gigabyte boards suffer from this quite a lot. The only solution is to get a new board. My father had a similar problem and it did not happen on a consisent basis, but some days it would happen so often I couldn't even play a game on his system. Got a new power supply because in A+ training we were told that power problems like shutting off and random restarts point to the PSU. However, this did not fix the problem. He has since bought a new motherboard and has never had the same problem again.
NVidia cards tend to get rather warm and often cause this to happen. They are not operating out of range or anything, but the mobo thinks they are. I'm not saying this is definitely the problem with your board, but it could be. Check with the manufacturer to see if they have a video card thermal sensor on them. If it does, get rid of it. I never got the thing to be stable with an Nvidia card in it.
It also is possible, although unlikely, that you got another bad power supply. It has been known to happen. I would not cite the CPU, RAM, hard drive, or any card in the system as the culprit. Hard drive failures are often preceded by spurious data being written to the drive, corrupted files, extended load times, data that does not get saved properly, and in general Windows XP yelling at you about disk issues. However, if your system continues to restart and/or shutdown it will most certainly lead to OS problems and file system problems - NTFS is very picky about being shut down correctly, FAT32 not so much, but both will have major problems if you continually shut down w/o dismounting the drive heads. Data that was supposed to be written during the last burst is flushed to the heads in a last minute effort by the hard drive to get the data out. Problem is the heads are prepping for landing and are thus in the wrong sector at the wrong time. This results in the data being written to the wrong sector(s). Not good.
i have this same problem...very strange though....my computer kept hanging at first and making strange noises...i opened it up to look at the fans and they were working fine...i left the cover and the 'vent' off (the part that guides the air to the back). i forget why, i think i was hoping that it was a cooling issue and that would help (although i knew before hand that that doesn't allow the air to move the way it should)...my computer started turning off for no appearant reason.....so i put the vent and the cover back on, and now it hangs again....very very odd...
i as well have to reset the power switch...except i do it on the power strip......i tried without the power strip and plugginstraight into the wall but it continued to shut off...i would then have to unplugg it to turn it back on again...
^overheating
