I've a Nvidia GT 240 plugged into a Asus M2N68-AMSE2 on XP Pro SP2 driving a 22" LCD display at 1080/32bpp/60Hz. Till Sunday, everything was working fine with no hint of a problem. On Monday morning, when I switched on the computer and loaded Firefox, I saw a few of these 'discoloured' pixels in the page window. I could hover the mouse cursor over them but they would remain there. Scrolling, however, got rid of them. A few seconds later, a new set would appear. For the first couple of hours, this remained a low grade problem, total discoloured pixels were ~100 out of 2M on the screen. When I tried playing a video, there would be a crooked line of these glitches in the middle of the video window but which would then disappear after about 30 seconds, and the video would play fine for the minute I kept it on after that.
By early evening the problem got worse, now there were lots more of them in the screen - note that the desktop background never appeared corrupted and neither did the menu areas. Video playback was now a lot worse with glitches much more numerous and "dynamic". I hadn't overclocked any component in my setup yet was in the habit of monitoring temperatures, and the GPU always hovered around the low to mid-40s C, and so did the CPU cores and the MoBo and the HDD. The GPU drivers were Nvidia 281.XX. While searching for help, I came across advice to disable hardware acceleration, which I did, and voila! no corruption at all. I then increased the acceleration slider right one notch at a time, till the display remained fine. And it turned out that it remained so till I enabled DirectDraw and Direct3D acceleration.
I then updated my drivers to 301.42 but the situation remained the same - corrupt display with Direct3D On but fine with it Off. I ran dxdiag but the directdraw and direct3d tests passed successfully. So I tried out video playback again and a weird thing happened: the video played fine but after about 30 seconds, it stuttered and then the computer froze with no response from the KB or mouse. Checking event logs afterwards showed a parity error related to nvgts.sys. So I went back to Direct3D Off mode and it was fine again. On further searching, I read that the artifacts could be due to bus transfer errors, so I took out the card and brushed off the accumulated dust off the PCB and the connectors. But the problem remained when Direct3D was enabled, and that's where it stands now.
Update1: Now there's occasional glitches even in no-DirectX mode when I scroll certain webpages. The glitches disappear a couple of seconds after I stop scrolling.
Update2: Recently, I started getting more frequent occurrences of the glitches while scrolling so I removed the card and switched to the onboard Nvidia chip, and there are now no problems with any level of acceleration and with the same installed drivers to boot. So I guess this rules out software or motherboard related issues, leaving card hardware (likely video RAM) or bus connector as remaining candidates. Prudent to just RMA the card now. I do have one semi-related question : when I would play a 640x360 video in 1080 full screen with no DirectX accel, it would appear pixelated i.e. not anti-aliased, but it automatically appears smooth with DirectX on. For future reference, is there a way to force this at all times? If it's media player specific, I can use KMPlayer or PotPlayer.