Unit not functioning properly. Can't us says there is R/W unit error

May have accidently deleted part of operationg system.  unable to restore.  unable to retrieve data or doewnload.

External USB drives do not come with an OS.

What is the model number of the drive you have?

It the drive is not seen by the computer, try the steps provided on the link bellow:

http://wdc.custhelp.com/app/answers/detail/a_id/1164

have you tried another usb cable? sometimes an r/w error can be caused by a bad cable.  of course I’m assuming you’re talking about an external usb drive.