It has been 6 months since I got a Prestige 500GB Iomega External Desktop HardDrive which requires both a printer USB cable and a wall charger. One day it randomly stops working and doesn't show up on my computer. The Hard Drive sounds right, but it is no where on the computer: not in device manager or disk management. I contacted Iomega, and they sent me another power supply which does not work either. Suggestions?