put the car in park with the handbrake released, see if the car will roll. Do the same with the car in drive (engine off) and see if there is a difference. If there is, you have a tranny problem, if there isn't your driveline or differential might be the problem.

can you check your shift linkage?

Also, when was the tranny fluid replaced last.

Finally, if one of the CV joints failed in the back or came loose, this would cause no motion unless you had a lsd or locker.

Strange...

Have a Hopefully Happy New Years!

Adam