XFX 4870 resetting itself, help

I installed a 4870 into my system and now it keeps resetting itself when i go into some games like crysis for example. Ive had to underclock the card in catalyst control centre for the games to run properly which is unacceptable. I also tried to updated to 9.4 driver but when i install it and restart the pc, i go and check the driver in device manager and it says its on 8.6. i thought the psu may be a problem but not sure. i used to have an xfx 7600gt installed and didnt have any problems. i did my best to delete all old nvidia files including drivers.

the system is:

E5200@ 3.0ghz 10x300
2x1gb ddr2 800mhz corsair xms2
asus p5ql pro
500W Storm LPJ19-25
1 sata hdd
1 ata odd

try using driver sweeper (http://downloads.guru3d.com/Generic-Utilities_c8.html) to remove the nvidia drivers completely.

if you really want to remove the drivers with 100% certainty you could always reinstall the os.

the 4870 i believe pulls around 268w at load, consider upgrading to a higher powered psu, or at least borrow a friends to test the theory with.