I have just tried to install LR 6 as a standalone (NOT CC) installation. I put in my new serial number, it told me it could not find any compatible products for the upgrade so i had to put in my LR5 serial as well. then it would not launch but told me I had to download Adobe Application Manager as well - despite choosing the non CC download I got something plastered with CC links. Ran it anyway. LR 6 now opens without warning messages but when I go to the Develop module the image space is just a blue rectangle with a white diagonal cross. What is wrong - I've done everything by the book and I have a fully paid for licensed product but it won't work !?!?!?!?
Updating my integrated graphics driver didn't work but unchecking 'use graphics processor' did the trick
I encountered a similar problem after upgrading to Lightroom Version 6.8. I could enter the Development module, but when I tried to leave (to go to the Library), Lightroom just hung forever. My solution was also to uncheck "Use Graphics Processor" in the Performance tab of Preferences.