Flaky Power Supply, or external factors? (Round III)

In a previous post, after the crashes returned despite swapping in a new power supply, I disabled the onboard sound, and that seemed to fix it for a while. But then the crashes returned again. By this point I'm thinking this is ridiculous.

Then I noticed my desk lamp seemed to be flickering a bit. It occurred to me that maybe I was getting dirty power, especially since this room has had power problems in the past (I run all my monitors on an extension cord from another room, because I sometimes get ripple in the picture when plugged into the outlets in this room).

I ran an additional extension cord from another room and hooked up the PC that has been crashing. Then I re-enabled everything I'd disabled - primarily such features as onboard sound and AGP fast_writes. Firing up the PC, I started Prime95 up, launched the Mozilla web browser, and got Winamp playing some music while I browsed. That usually suffices to crash it quickly. No crashes in the past several days.

Darn dirty power. I think that might be what it is. I've factored out just about every other piece of hardware, except for the motherboard, and given the variability of the problem and the complete lack of effect adjusting motherboard settings has, I suspect that it may be outside stimulus.