Hi T,
peel back the rubber boots at the end of the drive shafts, see if the pins are still in the shafts, they can snap after a time.
If they are ok, then it's time to look in the diff.
Don't forget the wheels will only drive and brake if both wheels are on the found, so to check hold one of the rear wheels put brake on and see what side locks and what doesn't.
Any probs give me a call, my number is on the MCB thread.
Steve