If you hooked the 2 blacks and 2 whites together and the other end was not connected and the breaker tripped, sounds like a short between hot and neutral or hot and ground.
Disconnect the white and try again. If it shorts now, then it is shorted to ground, also, if you reconnect white and disconnect thr ground and when you turn breaker on, if it trips, it is shotred to neutral.
Is there anything else on that circuit or not working?