I've been banging my head for a half an hour with a problem where the game starts fine but as soon as you reach the dungeon the video is black with only the mouse cursor, subtitles, text, menus, and automap are visible. The game is running, sound and all but there is no 3D image.
If you're a software developer like me you may have the DirectX SDK installed. If so you need to make sure you set the Direct3D runtime back to "Retail". I had mine still set on debug from my earlier software development work and forgot to change back. Ths runtime setting is in the DirectX control panel accessable from the Start Menu -> Microsft DirectX SDK (XXXX)-> DirectX Utilities -> DirectX Control Panel. On the Direct3D 9 tab be sure the radio button for "Use Retail Version of Direct3D 9" is selected. This made all my problems go away.
You do not want to play games using the Debug runtime as it decreases performance and can cause some games to crash.