The video card in your computer is one of its most important components. The card controls all the video processed from your motherboard to your monitor. All the graphics you see on the computer monitor from the basic desktop to the graphics in the games you play rely on the video card to work. Without a working video card, your computer is essentially useless. Computers cannot show you anything unless the data sent to your monitor via your video card can make it to the monitor.
Turn on your computer. If your computer does not even turn on there could be a multitude of problems with your computer, of which the video card is only one. You can try replacing your video card at this point but it could be several other problems such as your motherboard, memory, power supply or even your hard drive. If you replace your video card and the computer still will not turn on then you will have to replace other parts of your computer to get it to work.
Check your screen. If it stays black but the computer powers up, then it could be a problem with your monitor or your video card. Follow the next step if your monitor shows a white screen or lines on the screen when you start up as well. If the computer starts up then skip the next two steps.
Shut down your computer and try plugging it in to a different monitor. Start the computer again. If it starts just fine then you will need to replace your monitor. If it starts but the screen stays blank, try replacing the video card at this point. If the computer still shows a white screen or lines, follow the next step.
Turn off your computer. Open your computer case. Remove the video card and unplug it from the board. Plug the video card and close your case. Restart the computer. If the computer starts up fine, the card had just come loose and is probably okay at this point. If it has the same problem, try replacing the video card. If your video card is integrated into your motherboard then you will need to replace your entire motherboard.
Try using your computer and see what happens. Generally if your computer starts and the video works for a period of time then it might point to some other problem. If you are running Windows, you can check your card by clicking on the Start menu. In the Run box or Search if you are using Vista, type dxdiag. Choose the "Display" tab. If your card is working fine, it will say so in the dialog box; if there is a problem with the video card, it will list the problem.
If you think you are having graphics issues you can check the manufacturers website for newer drivers. Installing newer drivers will take care of most bugs that may cause video problems on your computer.
If your computer starts up fine but turns off when you play a game or scrambles the video after a few minutes you may have a virus. If your computer feels very hot after this happens, you may have a power supply or fan problem. These problems will need to be fixed immediately to salvage your computer.