Symptoms of a Bad Graphics Cardby Rob Senn
A graphics card can be damaged out of the box, by excessive overclocking or by other physical damage. Even if the card appears to be working fine on the desktop, a damaged card may begin to show errors in 3D games. It's important to know the warning signs so you can return or replace the card quickly.
A common symptom is known as "pixel popping." When this occurs, a single pixel of a 3D image seems to explode outwards, taking up large parts of the screen. This is typically a sign of damage caused by overheating.
This symptom even shows up on the desktop. Single pixels will turn green (or sometimes other colors), sometimes at random and other times on areas of the screen with intense colors or shading.
In graphics intensive games and applications, damaged graphics cards can sometimes cause the entire computer system to hard lock, requiring a manual restart.
Flickering and Black Screen
Damaged video cards can sometimes cause the screen to flicker rapidly, and eventually it may stop displaying all together. Sometimes the card will begin displaying again after a restart, although occasionally the black screen is permanent in the case of severe damage.