Assumptions:

1. One hard drive (you do not yet know which one) and associated cables and computer port are good.
2. The other hard drive is receiving at least some power which means the MVHD internal harness is definitely good and the external USB cable is probably good (later troubleshooting will verify this if necessary. This means the most likely problem is either the hard drive or the computer.

Do the following:

1. Disconnect hard drive "A" from the MVHD internal cable "A".
2. If the hard drive disappears on the computer then the hard drive you disconnected was the good drive. Pull this drive out and set it aside then.
   1. Gently pull the hard drive out of its foam and hold it up to your ear.
   2. If you absolutely nothing, the drive is the problem.
   3. A soft ticking, clicking, or beeping sound indicates insufficient power from the computer USB output. Connect the Auxiliary Power (USB pass-thru connector) of the external USB cable to another USB port on the computer. If that does not solve the problem try the other USB cable in exactly the same hook-up. If that does not work try turning off USB power management then reboot the computer. If that does not work try connecting to a different computer. If that does not work the drive may be the problem.
   4. A gentle whirring or "ocean" sound means the drive is getting enough power and all hardware appears to be good. The problem is in the computer operating system. Try turning off USB power management then reboot the computer. If that does not solve the problem try a different computer. If that does not work contact Customer Service for assistance.
3. If the hard drive did not disappear from the computer then the drive connected to MVHD "B" must be good.
4. Replace the first hard drive and reconnect it to the internal MVHD cable "A".
5. Disconnect the hard drive from internal MVHD cable "B" and set it aside. The hard drive should disappear from the computer.
1. Gently pull the hard drive out of its foam and hold it up to your ear.
2. If you absolutely nothing, the drive is the problem.
3. A soft ticking, clicking, or beeping sound indicates insufficient power from the computer USB output. Connect the Auxiliary Power (USB pass-thru connector) of the external USB cable to another USB port on the computer. If that does not solve the problem try the other USB cable in exactly the same hook-up. If that does not work try turning off USB power management then reboot the computer. If that does not work try connecting to a different computer. If that does not work the drive may be the problem.
4. A gentle whirring or "ocean" sound means the drive is getting enough power and all hardware appears to be good. The problem is in the computer operating system. Try turning off USB power management then reboot the computer. If that does not solve the problem try a different computer. If that does not work contact Customer Service for assistance.