I had a issue with the Epson GT-S50 Scanner as well. The scanner window would open in the task bar but not on screen. I tried removing and reinstalling the drivers but that didn't work. Tried Alt+M to move the screen but that didn't help.
My solution: I used Windows Key + Shift + (directional keys a few times) the scanner window eventually opened up on screen.
Needless to say this is very frustrating.