Continue to fiddle, I tried swapping dimms. system worked. swapped back to original dimms. system works. I'm unable to justify three failures at same time: bad psup fan, dead cmos battery, and badly seated dimms. PC was located in room without access overnight and showed no signs of disruption. 5 other computers working fine. No storms or known power glitches. I'm betting I'll se this again. Anybody got any ideas?