Alright, so me and my brother both have the same hardware. We both have a HD4870, 4gb ram. The only difference is the processor and the power supply. I have an E8500 @ 3.16GHz and he has an E7400 @ 2.80Ghz and his games work better than mine. He uses Windows XP and I use Windows Vista (because XP and Win7 showed me BSOD). I was using XP and the games ran bad (installed with a dirty cd, showed me errors all the time). So do you guys think it's the problem with the power supply or windows?
You've failed to mention what PSU you have, also update all of your drivers, XP will most likely run games better than vista, but XP won't supper DX10 or 11.
And you somehow must fail if you get BSOD with Windows XP and 7.