Try switching "OpenGL" to "Direct X" or visa vera. Have you installed the latest drivers for your video card? Does it happen in one or two sessions, or is it in all sessions??? Did you download the sessions from the DLS or from 3rd party sites? (if it was from 3rd party sites, then you often have "missing dependencies")... Have to applies the latest service pack/patch?
Can you supply us with more detail please?
Cheers, Mac...