OK on a nicer note.. if the center diff gears are not meshing up it would more than likely have stripped them out. To check the diff set the buggy on a table, hold the spur gear so the diff cant turn and then try to push the buggy. It shouldnt roll.
I will take a wild guess and say that the out drive set screw on the front or rear diff loosened up. Its very common. The drive shaft will spin but the power isnt going to the diff.