Hi there,
We got this sort of thing quite regularly, the fix for us was for me to cut someone's fingers off...
But slightly more realistic is to ensure that before people close their remote access session they have to re-enable the scheduler function. This was the step that seemed to be missing every time we ended up with a 'dead' screen.
Essentially, take your USB stuff out to the screen and restart the scheduler and it should then be accessible from the server app... Or of course you could just take the nuclear submarine approach and turn it off and on again!
I will however say that the above seemed to work for us (and every time since highlighting it the phone calls have been more along the lines of "I did it again" rather than "I can't access the screen") but you may in fact have something different going on...
Hope it helps nonetheless
Greg