I had such issue too. Bumping a bit voltages on CPU, SB and NB helped on my rig. I donno why 

My Computer
- OS
- XP
- CPU
- E7200
- Motherboard
- Abit IP35 Dark Raider
- Memory
- A-Data Vitesta EE+ 4GB
- Graphics Card(s)
- ASUS 4850 + Accelero S1
- Sound Card
- CREATIVE X-Fi Gamer
- Monitor(s) Displays
- HP w2207h
- PSU
- Corsair VX450
- Case
- NZXT Apollo crafted
- Cooling
- scythe