what cause this problem?

[HooHee]

symthoms:
- games lag, higher lag the higher percentage rate of disconnect
- 50+ frame rate still feel clunky
- system reboot itself every 10 hours
- when press to turn computer on, 50 percent it wont display monitor


spec:
athlon64 3200+, 2.75gb ram, X850 XT, xp home 32bit





- so after replacing 400 watts dynex to antec 380 watts green and still the same... not the psu.

- after increasing ram amount and still the same.... not the ram.

- after cleaning dust out of the X850 XT and still same.... not the graphic card.

- after internet fine yet it disconnect while other computers dont.... not the internet

- after updating catalyst driver from 8. something to 10. something and still same.... not driver



what else could be the problem? overheat? cpu need thermal paste renew? mother board expiriing?