mouse key corrupted

Mouse left key impaired
While editing a piece I accidentally held down a key combination including the windows key (win) and maybe ALT or maybe Z+ALT. Now the left mouse key (LMK) is impaired. It does not grab a panel (eg mixer) to move it, affect any of the options within the panel nor close it. Toggling win on and off restores some functionality. To use the mixer I have to toggle win, move dial to new setting, slide cursor off mixer panel and left click to lock new setting and allow cursor to move to new dial.
There are more quirky problems.
Restarting Musescore doesn't fix it. Rebooting didn't fix it. Reinstalling didn't help.
system: (MS2.1.0 rev 871c8ce Win 8.1)