A graphics card is vital to the function of your computer, and in failure can cause everything from minor screen artifacts to a complete inability to start up your computer. Causes for failure may vary from fan problems to overheating as a result of worn thermal paste or poor ventilation. If in doubt, you can try to troubleshoot to see if your graphics card is the problem by starting your computer in safe mode, checking for consistencies with graphics issues and checking your card for physical damage.
When a graphics card starts to fail you may notice artifacts, screen tearing, discoloration and other problems. If you're playing a game, the screen may flicker and some objects may change colors as you move. You may also see similar problems outside of graphics-intensive programs. Play a few different games and run various programs to see if the graphic errors are consistent. If not, it's possible that there could be a compatibility issue between the program displaying the problems and your graphics card.
Computer Won't Start Properly
Whenever you turn on your computer, it goes through a power-on self-test routine. Among other functions, it initializes BIOS, verifies your computer's memory and identifies your computer's devices and hardware. If your graphics card isn't working correctly, it may prevent your computer from completing the POST routine, which means your computer won't start correctly. If your graphics card is failing, your screen might remain blank as your computer turns on, or you might hear a series of beeps. If your display isn't working, try booting into safe mode. If your screen works in safe mode, your problem may lie with the graphics driver and not the card itself. Check to make sure your card's fan is spinning; if not, this will likely prevent the computer from starting properly, and you will need a new card.
Effects of Heat
Computers can stand high levels of heat, but your GPU can get damaged if it gets too hot. This can happen if your computer lacks proper ventilation, which causes heat to build up inside your tower, but it can also happen if your card's thermal paste is old and not transferring heat from your card very well. This thermal paste can be cleaned and replaced, but it is delicate work; if your card is old and you need an upgrade, it may be more cost-effective to purchase a new card instead.