1991 Acura Legend transmission

While I was driving, my acura legend was in drive and stopped moving so I switch and try the other gears and they didnt work either but when I put it in park I hear a grinding sound from the transmission. I was assuming that my transmission went out, but when I talked to people about it they tell me it my be another problem because my car worked fine and had no signs of my transmission going out, it never slipped or anything it drove fine, but I suddenly stopped working the other day, I checked to see if my shift cable was hanging off but from what I can see it is still on. What do you think the problem could be and what should I do to fix it?