Found the solution to this problem.
Go to Control Panel/ windows features/ Media Features –> Windows Media Player.
Uncheck Windows Media Player, wait for several minutes for the menu to reboot.
After reboot, go to the same settings en turn Windows Media Player back on.

To my suprise it worked out right, just putting in a CD. and yes, Windows Media Player finally started playing.
Also with a data DVD, it opens correct with a menu or the options to explore etc.

Typical was that on another pc with the same W7 about 300 strings were found for Mediaplayer with Regseeker, where on the problem pc only 39 were found ??

After restart of Mediaplayer 49 strings were found, so some must have been missing.