i fix this issue by re-installing winDOHs.
fixed many issues exactly like this by doing that. get good pay from it too

but if that isnt the case it could possibly be heat related as the cpu is beginning to come under load.
i'm assuming it's either a 478 or 775?
dun worry. i run a 40gb IDE and a 160gb SATA so dont feel bad

my pc is rockin with a 3.4ghz dual core and 2gb of ram. perdy good for a machine made up of bits that people threw out!! never spent a cent on it!!