I can tell your from much knowledge: Don't remove the radio without removing the negative terminal cable.
It sound like it needs to be reprogrammed- don't panic. it is a combination buttons on the radio. I don't know them right now, but there are guys here that can lead you to them. If I am right, I believe it is because the battery was removed for all the time and memory in the radio cleared itself.
This is a thought I am having, but again there are much better tech assist guys on here that can help you.