2002 Ford Taurus Car Radio

Hi I have a 2002 Ford Taurus that sat for a while before I started Using it again. The radio wont work at all anymore. All the Radio does is say CALL on it and wont let you change anything but the time....is there anyway to fix this?? Before it sat the radio worked fine. I drove it once 2 months ago and the radio worked fine. Now its two months later, I had pulled the battery to charge it, now it just says call every time i start the car. I have never seen this problem before. How do I get rid of that and get the radio to work again