hey alioops -- general format for troubleshooting unstable computer:
Check for proper CPU (and other) cooling
Check power supply voltages (these are important, also note the +/-)
make sure system isn't overclocked. (some people dont know when to stop)
replace RAM
replace CPU
replace motherboard
move on to other, more obscure problems.

sometimes power supply voltages cause wierd errors. i had one with no -12v signal that ran fine, but the amplifier on the soundcard didn't work. i've had others that ran unstable because of incorrect +/-5v signals. +/- 12 volt signals don't have to be too close, but the +/- 5 volts do.