Is this something that just started happening? Does that drive have any images on it? Have they been imported into Lightroom?
Where in LR is it not being seen?
The import dialog should show it to you as a device to import from.
The Library grid will only show it to you if you have imported or relocated pictures on it.
Thanx all. There were no previous photos on the drive. When I put some photos on the drive, now Lightroom sees the drive.