Passport for Mac not showing up in Finder

I have a 2011 MacBook Pro which is not handling Yosemite well at all. One issue: WD My Passport for Mac no longer showing up in Finder. It does appear to be showing up in Disc Utility but when I do a verify or repair, I get an error message about the lack of a mount point. I cannot access any files on the drive and Time Machine no longer backing up. HELP please!!