Crazy transmission problem, any info??

Alright, we got this rebuilt tranny put in not too long ago and now it's dead... here's how it went:
Cruising down the highway doing mabye 80 in fifth... take the offramp and pull up to a stoplight. I go to take it out of 5th and it won't go... the shifter pulled down and all, but the car remained in 5th. Well seeing as it's a rather new tranny, I get a little pissed and pull on the shifter in an attempt to dislodge it... it comes down and makes this wierd clunk noise and all of a sudden all my gears are gone. amnit: The shifter will go into the "slots" for all the gears, but it's not engaging anything. It'll just sit there and act as if I'm in neutral. The weird thing is, the shifter slides without any effort... like it's not moving anything internal. So now I'm lost... anyone ever have this happen??! Easy repair?? I really don't feel like finding another tranny to put it in.

Thanks,

Hmm... I'll pull the shifter and see if I can tell anything from there. It feels like there's nothing attached to the shifter anymore... it slides in with no effort at all.