I have a somewhat complicated set up with two computers, a main and the backup, and a large number of peripherals that are attached to switches to move them between the two computers. The problem I have is on my main computer and concerns three USB external hard drives. They started dropping out about a week ago, one or two or all, and now all have dropped out completely. The three are plugged into a USB three switch and all three work on my backup computer and none show up on my main computer. USB pen drives show up on both computers. I have unplugged the external hard drives from the switch and plug them into two external hubs plugged into the main computer and they don't show up. The pen drives plugged into the same USB ports show up. I have plugged the external drives directly into the computer and they don't show up. I have plugged in the pen drives into the same ports and they show up.

The external drives do not show up in either the disk manager or device manager. I have checked the power managers and disabled any power savers.

I am at and absolute loss as to where to go from here. All the hardware been checked out work except for the drives themselves in the main computer. Everything works in the backup.HELP