you probably have EX, am i right?
5 & 6gen EX models have anti-thief device in head unit, so once power is cut to to it, it will not work untill you enter security code. you can get securety code for free at any Honda dealer, but they need to know serial number of head unit, to get serial number dealer have to take head unit out and they charge 1hr of labor ($60-$80) to do that. plus dealer can access Honda's data base only on weekdays.
so, here is what i'm tring to say, go back to body shop and tell them to make your radio (head unit) work again.