Ever since I put in this XFX 9800 GTX+ video card into my Dell Inspiron 531 (AMD 64 X2 5600+, 4GB ram), I've had some issues. Firstly, at random times small rectangles will appear on the screen, sometimes flashing and sometimes not. Attached is a screenshot showing them. They appear all over the screen, never in a certain pattern or in the same place twice. Also, the computer would automatically reboot, always while playing a game (nothing too intensive). At first I thought the card was overheating as it's idle temp was 61 degrees celcius. So, I increased the fan speed with RivaTuner. That brought it down to 43 celcius as idle. However, the issue still happened. So I tuned down the memory core of the card to 1002 mHz from it's stock 1100 mHz. That seemed to help 100% until the next morning, when the system showed symptoms again and auto-restarted while browsing the internet (first time for that). The screen went black, still showed the cursor (which changed to appropriate action cursors when moving it around the screen, as if it was recognizing it was hovering over text or a link), then the system restarted. I've tried older drivers from May, the drivers that came with the card as well as fully updated drivers. They all have the issue.
Any ideas? I don't think it's a heat issue, as the last auto-restart happened when the card core was at 43 degrees celcius. I'm almost sure it's a driver issue, but don't know how to fix it since all the drivers I've found give the same problem.