Up until a couple days ago this computer ran fine. Then we had a thunder storm and the power was knocked out. I'm unsure if the unit itself was left on or not, but since that day when I run something intensive the unit will shut it self off. When it does this I then press the power button to restart the unit the lights will come on for about 10-15sec and then shut off again having never even reached the post screen. I found a workaround for this effect, by turning it on and then switching the power supply off(there's a power switch on the back of the power supply)I then immediately flip the power switch back and press the power button on the computer the system will come back on and boot normally but will again power itself off when I run anything intensive. If I just leave the system alone it will stay on and not power off. I've no parts to swap out for this unit, so I can't narrow down the suspects but I'm leaning towards the cpu or system board. Specs WINXP 1GB RAM 3.2Ghz Pentium 4 Saffire X1650 512MB Pro I've checked all the fans and they're working fine. Anyone have some ideas

It's prob the power supply that's causing it. Regardless if it's turned on or not if the psu gets a voltage spike while plugged in, it could cause problems to your psu or even your entire system for that matter. But based on what you explained it seems to be your psu, because it only cuts off when a decent amount of power is being drawn out of it and playing a graphical demanding game will do that to a psu that that's either weak or damaged. I would try to swap out the psu first and get another one equal to that psu and try it and see if it still resets.

Could be esd damage to motherboard. "Best Practices", Event viewer, host file, perfmon, antivirus, anti-spyware, Live CD's, backups, are in my top 10