First thing, check that your power supply is supplying both 12v and 5v. If those voltages are there then you need to check that they are still at 12v and 5v when supplying 3Amps each. If the power supply does not supply the current (amps) then your box will not work and you need to get a replacement power supply (12v @ 3A and 5v @ 3A with the correct plug).
If you are getting the correct voltages under load (get it measured professionally if you don't have the equipment to do so) then you have a faulty unit that either needs repairing or replacing (hopefully you have a full backup of your data).