Use the File Manager program for your OS to search for the file name on that drive.
Is this on an internal or external drive?
Is the drive always connected to the computer?
What exact operating system are you using and what is the exact version number of LR that you are using?
It is an external hard drive - other catalogues on the same hard drive are listed - there is only one that isn't.
The hard drive is not always connected.
I am on Lightroom 5 on a Mac with El Capitan.
Use Finder, the Mac File Manager program, to locate that catalog on the external drive. Then double click on it. You should also be able to use the Open Catalog dialog window in LR to browse through the hard drives connected to your Mac to find it on that external drive.
The Open catalog item in the menus (Not sure if it is under File menu item on a Mac) brings up a version of the OS X Finder program that should list every drive connected to your Mac.