Could be something else. What kind of motherboard/which chip set? I was a pretty avid builder for a number of years, and one of the things that kept me going was they way motherboards kept getting cheaper every time something new came along. And one of the reasons I more or less gave up in the last year or two is that so many of those cheap boards were failing after a couple years' service. Some were complete failures, others were lockups and funky behavior like you describe that were sporadic and murderous to diagnose. All the boards were AMD with VIA and nVidia chip sets. Some of the failures were no big surprise - Albatron and ECS. But others were disappointments - MSI and EPoX. Then there is my ASUS A7N8X, still in use after something like 3 1/2 years, but even with it I occasionally have had trouble with memory that I can't explain - good Mushkin Level 2 that works for months then won't boot for a week then is OK again.