I have downloaded the new version from the Creative cloud, installed it, it would not launch, uninstalled it, redownloaded, reinstalled, still won't launch. LR 5 still works fine.
Yup, same thing here. Simply does not launch. LR 5.7 still works OK.
I'm running 64-bit Windows 8.0 on a 8gb Dell XP 15 (2013 edition). Tried uninstalling and reinstalling, 'run as administrator', 'run with graphic processor support' etc and still nada.
Open Creative Cloud Application Manager, log out then log back in and start Lightroom CC from the CC app manager.