You are still trying to use the trial version that you downloaded. It is the standalone version, and has to be licensed differently. It will be necessary for you to uninstall that version of Lightroom, and then install Photoshop and Lightroom from the creative cloud application manager. After you install Lightroom properly, it will open just as it did before the trial expired, except that you won't get that opening trial screen anymore. All of your work will be intact. And you will be able to start right where you left off. The Lightroom program from the creative cloud application manager is precisely the same Lightroom program. The difference is in the licensing. The creative cloud realize on your Adobe ID and password whereas the standalone version relies on a serial number.
Hi! Thanks for the reply... When I press the little button next to lightroom, there is the option of "Manage Application" but then underneath it it says "Uninstall Unavailable". So I deleted the whole creative cloud desktop app and reinstalled that, but still no change.