ATI 5850 has display issues in-game

Hi everyone, this is my first post on toms hardware, so here goes.
I recently put together a new system, it includes:
-Core i7 920 Bloomfield quad core
-EVGA X58 Motherboard
-GSkill 6GB DDR3
-XFX ATI Radeon 5850
The problem with the video card is that when I play games, after some time the screen will get very patchy and pixelated. I did some experiments to learn more about this and found that this image only shows up while in an actual game. It does not appear if I am in a game menu, or any other screen on my computer. If I close out the game entirely and restart the program, the issue remains. Also, if I switch to a different game, the problem is still there. The only way I have found to eliminate this is to reboot my computer, which stops the screen glitch. These pixels also show up when I do 3D benchmark tests. I have my gpu overclocked slightly, and tried to lower it to stock levels, but the problem still happens. I thought it might be over heating, so I upped the fan speed, but even at lower temperatures of 50 degrees the video card has this reaction. Any ideas? Thanks!

Oh The Screens Turn into this:

my power supply is an APEVIA ATX-AS600W-GN 600W, its the oldest part of my system (a year and a half), as I did not upgrade it along with the rest of the parts. Ill try underclocking the gpu also, if that works then should I RMA the card? Because it's supposed to be able to overclock quite well

Yea both ram and cpu are working quite well, cpu is overclocking nicely, although im not pushing it very hard until I get a better heat-sink. I'll try underclocking and testing for artifacts to isolate the problem

well, even if the PSU isn't the problem, it should still be changed, APEVIA is known for very bad PSU's

Let me guess, you had an nvidia card and then you just slapped in a ATI card and expected the drivers to not conflict?

naw its an entirely new build, minus the power supply, I wouldn't expect existing nvidia drivers to not conflict with ati drivers lol. The ati drivers are completely up to date also. i have been testing it more, and it has this issue at stock speeds as well, at acceptable temperatures. so I think i will RMA it to XFX

Eeeeewwwww apevia sucks liquid crap. Get a better psu.

i have met the same visual problem on my old 8800GT, and I believed it is the problem for the onboard ram on the display card, you better ask for a replace asap.

My old card function without problem for 1 yrs. One day, the display card fan don't turn anymore but i don't recognized it, i used 3 more days and the display halt every 15mins, and the screen become a bit "blur".

I then replace the fan, and the halt problem is solved. But the in-game screen oftens (not all the time) got the same pixels box problem. After 3 more months, it because always got pixels box.

The pixels box always appear in the nvidia control panel test screen, and the pixels box show exist at the same place in the image everytime..... it make me believe one of the ram chip's circuit got melt down in the no-fan days, and it is finally died completely after 3 months declining.

Hope my experience can help.