By shifts, you mean the shifter runs the transmission through the ranges from Park to low gear?
First thing to check: converter to flexplate bolts. Did they get put back in? You'd be surprised how may times they get missed. If those are in place, you need to verify that the transmission is pumping fluid, assuming it has fluid.
The easiest way to do this is check the fluid level with the engine off. It should read considerably overfull. With the engine idling, check it again. If the level has dropped into the operating range indicated on the stick, that's good. If the level hasn't moved at all, the transmission is not pumping which would most likely indicate a broken pump gear/rotor.