I am having trouble on Mac OS X 10.10.3 have tried:
signing out of CC and signing back in
rebooting
removing all LIghtroom Preferences from ~/Library/Preferences
removing all Adobe Preferences from ~/Library/Preferences
removing all Adobe .plist files from ~/Library/Preferences
removing all Adobe Preferences and .plist files from /Library/Preferences
removing all .lockfiles from ~/Library/Preferences and /Library/Preferences
removing all files from /Library/Application Support/Adobe/SLCache
again signing out of CC and signing back in
I still get the Lightroom splash page when I launch Lightroom 2015 followed by the "Continue your trial" panel (26 days left still with not a single successful launch)... and no actual Lightroom.