It was downloaded from creative cloud and is showing as up to date. I am using it on a Mac. On clicking the doc icon (or directly via Finder) it briefly displays the splash screen then nothing. It was working previously. Os X 10.9.4 update installed recently is the only change. It won't launch in Safe Boot mode either. There is no lrcat lock file.
Neither of those helped.
Update, I uninstalled again and reinstalled direct from adobe not via creative cloud desktop. It's now working fine.