Transmission problems (after towing)

Well, stupid me, I towed my 89 volvo 760 turbo from washington state to virginia with a tow dolly. I put the car in neutral and went along towing. After the first day, I had to unhook it (b/c the nut came off the tow ball) and when I shifted the car it wouldn't move. The next day it seemed to work fine. Later on (after a flat tire) I had to take it off again. It didn't work again and this time, the next day, the transmission wouldn't work at all. When we finally got to virginia, we let the car sit for about a week and decided to move it to a more permanent spot that we can store it. We decided to try it just to see and it worked! My wife drove it while I lead the way. We drove about 10 miles (nothing above 40 mph) and when we arrived, the transmission stopped working just before we got the car into a parking spot. I tried getting it to work again but nothing. In summory:
- the vehicle starts up
- there are no strange noises
- the shifter moves back and forth (but won't "lock" into reverse)
- when locked into any of the drive gears it does not move when the gas is pressed

any clues on what I screwed up while towing?