begija,
Did the computer come with Windows 8.1 installed or did you upgrade from Windows 8 to 8.1, we need to know this in case the following suggestion does not help;
Restore the computer to a point that is before WMP stopped working, steps from MS below;
To restore your PC to an earlier point in time
Swipe in from the right edge of the screen, then tap Search.
(If you're using a mouse, point to the top-right corner of the screen, move the mouse pointer down, then click Search.)
Enter Control Panel in the search box, then tap or click Control Panel.
Enter Recovery in the Control Panel search box, then tap or click Recovery.
Tap or click Open System Restore, then follow the instructions.
Post back with an update for us.
TIP
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