I an using an iMac with lightroom 5 and a wireless external hard drive.
I can see the photos on the hard drive, but can not edit them in line room.
The external drive is listed in light room but it shows it "off line".
As far as I know all actions with the photos on the ext. drive have been done through light room.
What do I need to do to reconnect light room and this external hard drive?
Is the drive properly connected?
Is it shown in Finder and mounted on the desktop?
I suppose the disk is not connected and Lightroom shows it's cache pictures. That's a way to work with pictures and edit them, without having them physically attached to the computer.
You need to look at the OS level (Finder), if the disk is correctly attached to your system, as 99jon suggests.