How can i fix my samsung er-5100 cash register?

While turning the key for the till to make a z report, one of my staff pressed a button as they scrolled passed x, this resulting in only the numerical numbers and change buttons available, so as staff do they tried to fix it, only making it worse, when I found out I reset all totals and counters, but to no avail, I then tried an initial clear, this worked, but now the screen shows closed and there is no reaction on the till, could someone please tell me how to open the till to be able to use it again.

Many Thanks