Need help

[Matas]

I have very strange problem. Two weeks ago my computer started automatically turn off, and after shutting down it started to peep. I took my PC to PC-fixer and he diagnosed that RAM contacts were dirty and RAMs sometimes were not contacting with motherboard. About 5 days after I get mine PC, it started to peep again. So it seems, that the problam wansn't the dirty RAM contacts. I don't know what to do. Any suggestions?
My PC: Athlon 64 X2 3800+;
DFI LanParty Ultra-D;
GF 7800 GT;
Corsair TwinX2048C2
X-Fi Fatal1ty FPS.