i HAVE AN EXTERNAL DRIVE BUT CAN'T SEE THE DRIVE IN MY PC
Could also be that it is trying to share a drive letter with another hard drive in your pc. Windows seems to like to give external drives and flash drives the letter F:. If you are like me and already have an F: drive the new drive will not show up until you change the drive letter in Disk Management.
Little more background would help with a diagnosis, it could be several things besides the 2 named.