Upgraded to Lightroom Classic 7.2 and now will not open. I've tried uninstalling and reinstalling fresh and still will not open. I've tried signing in and out of CC.
It does not even reach the stage of showing the welcome banner. It just hangs never to recover.
I'm using Mac OS 10.13.2 on an iMac (Retina 4K, 21.5-inch, Late 2015).
Try to start LR while holding down the option key and create a new catalog.
Does LR work now?
I've now resolved this issue through the support of the excellent web chat. It was a problem with the Lightroom Preferences which had to be deleted.