File won't play or has no sound or has no video or looks bad

Check the DirectShow settings for the file type in MC Options/Playback/Video/DirectShow. If it is checked, uncheck the filetype for playback in DirectShow. Or vice versa.
Under DirectShow settings, try changing the Video Renderer used.
Also see problems caused by other hardware and software in our Wiki topic called "Weird and wonderful (crashes, memory, stability,...)"
If MC can't open the file with DirectShow, it may be imported as the wrong media type. This can be edited in the tag for the file.

DirectShow a complete mystery?

Please read the DirectShow Guide on this wiki.
Consider installing CCCP.
Some DirectShow filters don't work.
If you're having trouble, try playing the file with Windows Media Player. WMP uses DirectShow and results will be identical IF the filters used are the same.