There are several factors that can cause problems with your video.

• Check and make sure the acceleration is not set too high.
• Make sure you have the latest drivers for your make of card, also it's a good idea to download the latest drivers from the manufacter's website.
• If your screen is flickering, try setting the Desktop area to less by right clicking on a neutral area on your desktop.  Choose properties and then the settings tab.
• If you have a black screen, you most likely have the wrong drivers for your video card loaded.  Try starting up windows in "safe mode" and putting the standard SVGA drivers back in.