A reason might be that you have another game or webbrowser running in parallel which uses 3D accelleration for its rendering too, but Direct3D instead of OpenGL; and two applications using competitive graphic accelleration APIs may cause issues. For me it often happens that Firefox using Direct3D goes completely black when PlaneShift runs.
Another reason might be that you have an outdated graphic driver, or a graphic driver which does not exactly match your graphic hardware, but issues become apparent only when using an OpenGL accellerated game, not when using other APIs.
Now you tell us details: Which hardware do you have, especially which graphic chipset (use e.g. HWiNFO32 to detect that in detail), and which driver version and origin (via Microsoft Windows update, or via the graphic card manufacturer's website)?
