F'An,
The first thing you should check is the fuse. It should be up under the dash to the left of the steering wheel, if it's like my '96. If not, it'll be listed in the manual. Find and open the fusebox, locate the specific fuse for the rear defroster, then pull it out with your fingers and look at it. It will be a crooked piece of thick aluminum wire inside of a thin plastic sheath, with a couple prongs sticking out, and if the wire inside is broken, there's the culprit. They burn out when overloaded, and that's what they are there for, to protect the circuitry. Take it down to NAPA or somewhere and get a new one and poke it in there. You may actually even have a spare right there in the fuse box lid. USE THE RIGHT SIZE!
If that's not it, check each wire on the rear glass very carefully, because if anything has broken a wire (they are on the inside of the glass) it will have broken continuity and won't work. That would mean a wire replacement, and a glass shop is the place to go. Open the Yellow Pages and call around. DO NOT, UNDER ANY CIRCUMSTANCES, GO TO THE DEALER! Even if your engine blows up, for gosh sakes, don't go to the dealer. There are lots of honest independent mechanics out there who can do the job perfectly well for a lot less money. So, even if it requires a change of wire, or a repair, it shouldn't be much. What are they called? I don't know, but they're just thaw wires, and work on electrical resistance just like a toaster or any electric heating element, only much lower voltage.
Best of luck with it.