ober is correct. But changing the slots probably will not help, since the new ram will still have to match clock cycles with the slower ram. Also, you may have purchased RAM which was too fast for your MCC(Memory Controller Chip) / FSB. You also may have purchased RAM which is defective. Usually you would receive a Parity Bit error or messages from windows saying "ERROR blah blah, disable shadows and caches... if the RAM went bad. One thing to never listen to is Disable Caches, if you do then you've just turned your PC into about 1/10th the speed(although speed remains, it just 'sits' while the RAM is refreshing) it could've been because the computer uses the caches to store codes to, then when a wait-state stops the CPU from accessing the FSB then it can continue to execute code rather than waiting 10 clock cycles. So your problem may simply be faulty RAM, or in some odd circumstances, the problem could be the RAM Interface (common term used to describe the RAM slots).
