How can I fix my Royal 480nt?

I have a Royal 480nt cash register. I plugged it in and went to ring something up, and this is sort of what came up when I pushed the first button "16559". I managed to play with it and get it to stop doing that and display actual numbers that I type in. However, I type in the price... fine, then I go to hit a button such as 7/27 (i forget what the key is labled but it is like that) when I hit that button to make that charge, an E meaning error comes up. It wont X or Z out. I took it apart to the circut board and i cannot see what is wrong. Can anybody help me? Do I need a WHOLE new circut board or is it something simple? Thanks, Jay