Hi WILLYOU,
Has it always done this, or just recently? If just recently, you might see if a System Restore using a restore point dated before the problem started can help.
Check to make sure that you have the latest video and monitor drivers? You may need to uninstall them in Device Manager and reinstall them again in case they got corrupted.
Try different monitor type cables to see if you have a bad one. (EX: DVI, VGA, HDMI, etc...)
Hope this helps,
Shawn