It could be that a Windows update has messed something up. Some people have had to upgrade their video drivers to fix such problems after Windows updates. Also make sure any Windows updates have completed properly by rebooting the PC.
If that doesn't work, try backing up MC, uninstalling, reinstalling, and then restoring the backup you just made including settings. Then aim here is to get MC to redownload all the components it needs play videos and so on.
Another thought; Are you running Theatre View using Direct3D or OpenGL?
The setting is at "Options > Theatre View > Advanced > Use OpenGL Theatre View". If ticked, untick it and try again. If unticked, tick it and try again. I use OpenGL, and it is the future for Theatre View anyway, so worth a try.