The earth wire may have come off behind the radio, if so you may be able to see where it was hooked up. ... or the active wire may be on a separate fuse behind the radio. Double check the main fuses again first though!
Even if the fuse was bad, there would probably have been some problem that caused it to go. Fuses are a protective device designed to prevent fire in the event of a short. However if the fuse is good and you can measure a voltage at the end of the cable then you likely have a problem inside the radio which could be anywhere, but the first place to look would be the switch. You may be able to jump the switch out of the circuit which would mean your radio is on all the time that's what I did on my jeep. Probably the best thing to do is just buy another one though.
Another problem spot is in the steering column where the radio wires are connected to the switch. Just repaired a dodge where the steering wheel adjuster caused the wire connections to short when the steering wheel angle was adjusted.