First check your monitor and video card, whether the connection is loose, if not, maybe the problem is in the video card driver, then try to update your video card http://www.pcdriverhelper.com/Video+Card.html
If it still can not fix your problem, maybe there are some registry errors in your system, you need to fix these registry errors http://www.registrygenius.com/.
Last but not lest, if it is because virus infection, you need to clean these virus also http://www.bestspywarescanner.net/spyware-list/Worm.html.
Emaily Bake, November 2010