I borrowed my friends external harddrive to get some music and movies off of it, but when I plug it in my computer can't detect it. The power is on and the cords are plugged in. I tried to use a different external and I couldn't see the other one either.
If it's a MyBook, we have had issues with then that when connecting to a PC where they haven't been previously used they never show up in "My Computer". We always have to go to Computer Management (right click My computer icon and click Manage). Then go into Disk Management and assign it a drive letter. It may also need a driver off the CD that came with the drive.