Graphics card issues

Hello. :wave

So here's my problem. Since a couple of days ago, I've been losing the signal to my monitor. Usually it's a couple minutes after I load up a game. The computer and sound keep running, however the sound starts buzzing after a couple seconds. I live in an apartment that gets very hot in the summer, and the room that the computer is in doesn't have air conditioning, so I though it was an over heating problem. However looking at the temps, they're not that high. The CPU get to about 40c-50c on average. The GPU gets to 65c-75c. While thats high, I've heard people say GPU's can handle that heat. So I'm completely baffled as to what the problem is. I've tried blowing the dust out of the computer, as well as putting a house fan next to it with the frame open.

The Graphics card is a ATI Radeon HD 4600 series. It's been working for about a year and a half now.

The computer is a Gateway SX2800-01.

Processor: Intel Core 2 Quad CPU @2.33GHz 2.34GHz
Ram: 4gb
Windows 7, 32 bit operating system.

I'm a bit noob at this, so not sure what other information you're gonna need. Just ask. Thanks!

 

Heat can affect more than the CPU and GPU. Does it do it first thing in the morning when still cool?

I always like to start with known good power. So if me, I would swap in a spare, known good PSU, or have that one tested.