RE: EXTERNAL HARDRIVE..

Disconnect the USB drive
Boot to Safe Mode (F8 at boot), then open device manager (Right Click MY Computer, Properties, hardware tab, devicemanager button) then find the USB Root hubs and delete them
Reboot in the normal mode, go back to device manager, usb root hubs, right click each, properties, power management tab, uncheck the check box to let windows power off the hub (On by default)
reboot, connect drive, see if it detects.
If it doesn't. open Disk Management (Click Start, click Run, type compmgmt.msc, and then click OK.
In the console tree, click Disk Management. The Disk Management window appears) http://support.microsoft.com/kb/309000
and see if it is seen then but has a conflict with the drive letter.
If that doesn't resolve, try drive on another system.