It sounds like it might be a Samsung / Sam4s register if it says "CLOSED" on the display. If so, you need to enter a clerk code and press the clerk button. The default is 1 so try 1 then CLERK or CLK# to log in to the machine.
If you need a Samsung manual, try here:
http://the-checkout-tech.com/manuals/cashregisters/samsung1.php
Registerman, June 2010