My 1997 plymouth voyager wont go in reverse.?

I was backing up to park my van and all of a sudden it sounded like i hit something. which i didn't because there was nothing behind me. so i continue to park and I try to reverse to fix myself but it wont move. The car will drive forward but wont reverse. i turned the car off and restarted it to see if it would work but it don't. Any idea what may have happened.? Overall the van runs perfectly..Has 96,XXX miles. Just bought it on wednesday.