I haven't used CC, so this is just a shot in the dark, but iTunes has a menu item where you authorize the program/account. Is there something similar in CC? It may just be a matter of your computer and the Adobe server exchanging a snip of code that got dislodged. If you haven't used it in a while, it could be that it times out or a software update to your system threw out something similar to a cookie. I'd check there first, and then try with Adobe's tech support or customer support.
Thanks for the suggestion! Today, I tried to launch it and when it prompted me to sign in, I did (as I did on other occasions yesterday) and it launched. Not the same result as yesterday, but it works now, so no complaints. (Other than I hate not knowing WHY something is broken and then fixed. WHY!?!).