Invalid Scores

> I have another score that I also tried deleting, that I deleted from the musescore website, but the score is still showing up in the program and saying, "your score could not be opened".
If you have deleted the score, it can of course no longer be opened.
What you see in the program are only links, it is the list of recently used files. This does not change when you delete files, which is only possible outside of Musescore. You can also delete these links, but then all the others in the list are also gone. This does not delete the saved files, only this list! You do this with "File / Open Recent / Clear Recent Files". Important: MuseScore cannot delete files, but only overwrite them with another file if you use "Save as". But then you will receive a warning.
Deleting the list is not a problem, because it is rebuilt when you open other files, e.g. with "File / Open" or from the File Explorer resp. Finder on Mac.
Simply ignore the deleted files displayed. If you open several other files, those that are no longer used will move further down the list.

Deleting the account and creating a new one carries the risk that you will no longer be able to access your cloud files. So make sure that you use exactly the same name and email address for the new account.

Reinstalling MuseScore is in almost all cases not necessary. If you run into problems but Musescore is still starting, use "Help / Revert to Factory Settings". If Musescore doesn't start anymore (on Windows) go to System Controls / Programs use the Repair function.

Addendum:
If you have a file that Musescore says is invalid, attach it here and we'll see if it can be fixed.