first my specs are.

AMD Phenom II x4 955 processor 3.2ghz 20gb ddr3 ram 4Gb Nvidia Geforce GTX 770 850w Corsair tx850w psu Gigabyte ud3 mobo Windows 7 professional

I recently uprgraded my vid card to gtx770 and upgraded my psu to the 850w thats in it now. i did a reformat with the installation of the new gpu and psu and started fresh and only have a couple programs installed (diablo3, nvidia control panel, wow, and steam). all drivers are up to date and everything is hooked up correctly.

the problem is it will randomly shut down. no blue screen. just turns itself straight off and reboots after a couple seconds. occasionally i will have to unplug the power cable from the psu for a few minutes then reconnect and it will start up. it seems pretty random. sometimes it does it when my pc is just sitting there on the home screen. and sometimes it does it during games. and sometimes it doesnt do it for days at a time. i noticed the psu felt hot so i put an extra fan blowing straight onto both the psu and gpu and neither feel overly hot after it shuts down now.

could it just be that it is a psu problem. the psu was taken from another machine but wasnt having this problem in that machine. i have seen a few articles online about gtx770 doing the same thing. but i havent found any answers or solutions. any help will be appreciated. im sure the 850w is enough to power my machine, im just stumped and ran out of ideas to fix it. i have even returned the video card for another thinking it might have been an issue with that particular card, but still gettin the same problem.