And is this a fresh install of the OS?
And finally, why not give a short run down of the machine before and after? If you changed the motherboard the classic gaffe is to leave an extra mounting post where there should be none.
I just recently upgraded everything but my GPU which is the Nvidia GeForce GT 520. My screen now randomly flickers, and makes the sound as if a usb has been unplugged. I'm running Windows 8, as I was on my last PC and it never did such thing. I tried the latest drivers for the card, and even some previous versions and nothing has fixed this. Gaming seems to make it happen just a bit more frequently, and sometimes it minimizes the game and flashes non-stop, resulting in a reboot. Other system components are i5 3570k 8gb DDR3 RAM, 1TB HDD, Any advice would be great because I'm at a loss. Thanks.