snagglepuss2k

I've run all sorts of program's to find errors with no errors, ran anti virus with no results, I've even formatted my hd & done a clean install of windows trying different versions with no difference. still the same

my pc keeps freezing it has no set pattern or time it just freezes, it can be anything between 5 mins to 2 hours. the only thing i can do when it freezes is restart using the power button no keyboard buttons do anything. my pc is using a gigabyte board amd athlon II x2 250 processor 3.00 GHz 4.00 gb ram 32bit win 7 any help would be appreciated thanks