How can I fix my Sharp ER - 3110 ?

I'm pretty sure that is lock mode isn't it? That means you haven't signed on. If you use clerk keys, slide a key into the clerk slot at the front to sign on. Otherwise try signing on with a PIN number and your clerk button.
If you need a manual, C-tech collective have all of the Sharp ER-3110 manuals here:

http://the-checkout-tech.com/manuals/cashregisters/Sharp4.php

Registerman
June 2012