Any number of things might have happened to the circuit board or components attached to it. Component broke off, PCB cracked, wire broke free, board shifted shorting something out.
Unless you have the expertise, schematics, and tools to diagnose you would be just shooting in the dark.
From the majority of what I have heard people are very satisfied with Uniden's flat rate repair program. They usually get the unit back with things done over and above what was actually broken.