I'm really sorry to hear you're having this problem. Could you please provide us with some information about your computer, so that we can confirm what may be happening, and hopefully find a solution?
In order to do this could you please run dxdiag (start, run, "dxdiag") and let us know the results? Please feel free to either post them here or send them to us directly via email at email@example.com
If you send them in via email we should have an easier time assisting you, as we monitor and respond to those more consistently.