Please be as so kind as to post your machine's specs, including what video card you have as well as what driver you're using. You can find your machine's specs rather quickly and painlessly by downloading and running the Belarc Advisor which can be found here: http://www.belarc.com/Programs/advisorinstaller.exe
Once you d/l, install and run that tool, you'll then be able to know everything that you ever wanted to know and much more about your computer! Oh joy right? Anyhow, after you find out what your vid card and driver are, we can then look deeper into what's causing this and perhaps even uncover a fix sooner than you think.
PS: When did you first notice this issue? Did you install or uninstall anything directly prior to this occurring? Answering these questions will most certainly help me in troubleshooting your issue.