Windows 7: Computer Randomly Restarting - Help!

Hi i have recently upgraded my custom PC with the following specs:

AMD Phenom ii x6 1055t @2.33ghz CPU
2 x 4gb DDR3 SD 1333 ram
gigabyte ga-970a-d3 motherboard
Seagate 1tb internal HDD
800w Ambiance Power Supply
Nvidia geforce 9600 gso graphics card
windows 7 home preimium 64-bit

I am having a problem with my computer randomly turning off and then restarting, it will do this without any BSOD error, I have turned off restart automatically of system failiure but this wont solve the problem. It will restart at completely different times e.g. while idle, surfing the web, playing games, or even sometimes on startup. All the parts are brand new and have all been tested, has a clean install of windows 7, i have updated and reinstalled all the drivers. I cant figure out what the problem is.

Any help would be appreciated.