Yesterday, I downloaded and installed Lightroom CC. Launching the program produced an immediate crash with no error message. I tried the fixes posted elsewhere on this forum without success. Subsequently, I contacted Adobe Support via Live Chat. The following steps took care of the problem and LR CC now opens correctly.
If everything goes as expected, you should see the Lightroom CC splash screen followed by a message saying, "Catalog upgrade in progress." You may also see a Keychain prompt: "Adobe LR wants to use your confidential information stored in [long-file-name] in your keychain." Select Allow or Always Allow (if you don't want to be bugged again.)
Once Lighroom CC is open, look for your name plate at the top left corner of the LR window. If you haven't already signed-in to Adobe CC you may be prompted to sign-on by LR.
Hope this helps.
This doesn't make sense... Step 7 just undoes what was done in Step 6.