Nissan Stanza with no reverse

I have a Nissan Stanza either 1990 or 1992 (I got it from a friend a week ago). It works great going forward, but it will not back up. When put in reverse, the motor acts like it wants to back up, but it stays still. When I tried to back it up by pushing, it still stayed still. The other drive gears, 1 and 2 stopped working. One day it just stopped backing up. Thanks. :D