It could be that the "brain" of the radio has locked up, try unplugging ALL power from it for a minute or two.

I doubt this will restore it, and even if it does - you don't really want a radio that is prone to this.
However, many microprocessor based devices will "lock up" if the power feeding them is intermittent. Any chance you have a bad splice in a power or ground lead?


Other than that...
As PNA said, it's probably time to return it.