how can I fix my Samsung ER-350 cash register?

The register has been working great until the other day when it somehow experience a power failure (it was never unplugged tho?)............Now I can't get it to do anything whatsoever. It is getting power but none of the keyboard functions do anything. Can't even get a number to come up, no-sale key, nothing. Turn it to z,x,and program mode and it just beebs continually. We tried to clear the programming and start over but not allowing that to happen either. Can't even turn the machine off without unplugging.........HELP!