Can anyone help me with this?

My 93 Sundance was backing up today and after I tried to shift (it's a
manual trans) into first, I was unable to push it into gear. I'm
unable to push it into any gear whatsoever -- 1 thru 5 or reverse. It
starts to move that way but don't go past the point where it would
click into gear. It will move side to side, but won't go into the gear
position.

Any ideas on what's wrong? How would I fix this?

Thanks!
Shaun