First, let me get it out of the way that I have already uninstalled and reinstalled Photoshop CC.
Clicking the "Open" button in the Adobe Creative Cloud portal no longer does anything. No error message, just nothing.
Trying to start Photoshop CC 2018 directly from the Windows Start Menu does produce an error. It says "The code execution cannot proceed because VCRUNTIME140.DLL was not found. Reinstalling the program may fix this problem." Unfortunately, reinstalling did not fix the problem.
It was working fine before. Last night I let it install a huge update for Windows (the kind that takes an hour or two, restarts the computer several times, and when it comes back it says something like "Hi, we've made some improvements to your Windows Experience" or whatever, something like that. Ever since then, I've had this problem. Also, I had Photoshop CS5 installed at the same time, and now that program says that my serial number is "no longer valid" and I can't run that either. I'm wondering if the update might have somehow stripped a folder privilege and the Adobe installer can't copy the needed DLL to wherever it is supposed to go. I dunno, but I need this fixed ASAP.
This helped half the problem. I can now run it from the start menu. However, it still will not run from the CC launcher utility. Nothing at all happens when I click "Open".
In addition, I've now discovered that Lightroom has it's own problems as well now. When I run Lightroom from the launcher, I get the error message: "Could not call C function: private_load_AgCoreTech". Also tried reinstalling LR, did not work. EDIT: Posted about this in the Lightroom CC Classic forum, since it's not really on-topic here.
It also did not fix the problem of CS5 no longer accepting the serial number after many years of working. It seems like the Windows update over the past couple days really bungled things up for Adobe software, hopefully a fix is coming soon.