I think you may have a hardware problem. First, it worked before. Second, in following this user forum for a few years, I've not seen anything like this repeat itself. Third, hardware problems such as disk failures can creep up gradually.
Just in case, you might try resetting the preferences. https://helpx.adobe.com/photoshop-elements/kb/preference-file-locations-photoshop-elements .html You could also try a complete uninstall and reinstall.
I hope I'm wrong about the hardware! Good luck. This won't be simple.
I will try the preferences tomorrow, as it is late at night now in my time zone. If I try the uninstall and reinstall, how do I do so without having to pay for the programme again? If it is a hardware problem, what exactly does that mean?
You can get a fresh copy of the installation program here: https://helpx.adobe.com/premiere-elements/kb/premiere-elements-downloads.html You will need the serial number that you paid for.
Hardware problems mean that some part of your computer is beginning to or has failed. For example, every hard disk drive will fail at some point. They wear out!