Toyota Celica rear axle seized?

I overheated the engine (separate problem) & still was able to drive & park it for a few days. I came back a few days later & the back wheels are locked up. The car is front-wheel drive. It is not the regular disc brakes (we took the caliper off one side with no change). We are pretty sure it isn't the emergency brake (it seems to be working fine) & it isn't the clutch. It goes into gear & "tries" to go, but the rear wheels won't let it budge more than a centimeter. Suggestions? It appears the rear axle is seized, but I have no idea how it could have happened or how to fix it. I can't even tow it!