Try3 said:
You answered your own question.

Reinstall Windows.
If you do modify it, make a new system image before each step & test everything after each step so you can see which one causes this problem & can undo it.

So to restore functionallity of one button i should reinstall the whole operatingsystem? Eh no.
Then id rather keep this button broken. I tought you might eventually have a clue where i can start searching for a fix.
This is only a tiny tiny part of the system, shouldn't be to difficult reparing it, if you know how. (Spoiler i don't)