I installed PS CC as a trial. My trial expired several months ago and I can no longer open PS. I now have a serial number but can't get to a point where I can enter it. I click on the PS setup and get a pop-up screen notes that my trial has expired. I click on the "license this software" button. I am then prompted to sign into my account. I do this and the pop-up says "no subscription found." My only option is to click on the "buy" button, and I'm certainly not going to do that. I have a valid serial #. Isn't there a location where I can download the software, enter my serial number, and validate it??? This is making me crazy! HELP!
Please confirm exactly which version you have a serial number for.
Photoshop CC is the Cloud subscription version of Photoshop and requires an active Cloud membership, paid monthly. You sign in with your Adobe ID. There is no serial number for CC.
Serial numbers were used for CS6 and earlier. As John said, all you need now is your Adobe ID and a valid subscription to license a CC application.
If you can figure out which version you have the serial number for, you can redownload that version and activate it with your number. Note that older versions may not play well with modern operating systems.
If you can't figure this out, you might consider the Lightroom and Photoshop | Adobe Creative Cloud Photography plan—it's only US$9.99/mo.