Could be the PSU have weak rails Nvidia Gpu's are greedy when it comes to power
I would have chosen a 600w or greater just because the specs say 500w will do doesn't mean it will actually work especially if the PSU is not a good one to begin with
I really don't know what causes your problem but I do agree with Solarstarshines. A quality power supply of 600 W or more with the proper amps. All power supplies are not created equal. Antec, Corsair, Seasonic are three brands that come to mind for quality.
XFX psus are also amazing :) if theres on thing you dont want to cheap out on its your psu
Temps are around 80 C when i play Diablo, and then it turns off
80C is hot, and most gamers don't like their graphics to get that hot, but i seen many video cards get that hot.
please edit your system specs so that we can further assist you.
System Info - See Your System Specs
Thats strange that you would be having a problem with the AMD FX-4100 and the HD-6770. As I have the same CPU and GPU in my rig and they worked fine right off the bat, with a dual display setup right on first time boot. Now its been said before if you don't have the internal speaker plugged into the jumpers for them then you wont get any beep codes. Here's an idea for you, Did you install your CPU your self? If so then it might not be seated in the socket correctly. You might want to double check that, as that is going to be a costly fix.
RitualJman
Temps are 80C on what? Your GPU or your CPU.
We also need you to fill out your specs so we can help you.
Quote