In my room NO computer passes prime 95, i recently moved house, and machines that used run p95 torture stable for days sometimes craps out in 5-6hrs sometimes 12hours. I've tested the house insulation and whatnot and it is more than acceptable, voltages are stable, never dipping below 1.65v *xp2700@ default, so far i;ve been through 3 motherboards and memory configs all to the same error, tried different psus from 300-550w all enermax/antec. Most of the time its a rounding error such as 4.999 instead of below 4 or something. Its very sporadic, most i've run it for is 13 hours without fail, cooling is excelllent, 52C max with an SLK-800.

[edit] 5v never below 4.89v and 3.3 usualy at 3.3 or 3.29v