here is possible help.

If you can play a record and hear faint music along with the loud hum you most likely have a ground disconected. Just make shure the volume control is down low to prevent damage to the speakers during this test or plug in a cheep pair of headphones.
basicily what causes this type of hum is when the ground is disconnected, the audio reciever is lead to pick up stuff like electromagnetic fields and other things in the air similar in fashion to a radio recieving a station. only difference is the record player and wires connected to it are acting as an antenna.
heres is a shure fire way to diagnose the problem

. disconnect the record players audio cables from the amp. turn the amp on. if you hear no sound at all, then you have officilally diagnosed the above by removing said antenna from the amp. If hum is still there, you have a problem with the audio amp.
hope my rambling helps and I wish you the best.