There is a good chance that it has moved away from screen. So per Solution Id: S-069899, try following.
With the measure properties command active, press Alt + Space. This would open the control panel for the mass properties windows
Now press M on the keyboard which would initiate the move command and turn cursor into a four-pointed arrow.
Now do not use the mouse but using the arrow keys from the keyboard, try to see if you can move back the window to the screen.
If this does not work then might have to change the registry key value for this window OR SOLIDWORKS itself.
Worked a charme thanks! (Think this was because I previously used 2 monitors)