1993 Toyota Camry Problem Diagnosis

My car had a leaking rear engine oil seal. The mechanic had to pull the transmission in order to make the repairs. After the repair, all was fine for about 3 weeks. While driving one day, I heard a grinding sound. I made to my home. Next time I attempted to drive, the car would not go into reverse but would go into drive. Later the car wouldn't go into drive or reverse. Each time I have tried to put the car into gear I hear a grinding sound. Occassionally I can feel the car try to pull forward when I put it into drive but reverse acts the same as it would in neutral. What shoud I do about this problem. Someone suggested that it was the torque converter. By the way, the car has now been sitting for a little over a year but it still runs fine.