What computer operating system is your Premiere Elements 11 running on?
Do you know where your originals are at this time? And, you find them on the hard drive?
If so, when you open your project and get the "Where is the file _____?" message(s), you point it to where you know the specifically named file is. You do these for each and every one of those messages. If you get lucky, responding to one of the messages, may trigger more than one at a time for file to project reconnects.
When you import source media into a project, all you get in the project are copies of the originals which remain at the hard drive save location. But the copies in the project need to trace back to those originals where they were at the time that they were imported into the project. If you moved, deleted, or renamed files and folders that you imported to the Timeline after the project has been saved closed, you are going to run into the source media-project disconnects.
When you reinstall a program, you should not lose the project file. But that project file has to trace back to its source media which apparently got disconnected.
Where was the source media for the project stored? If external hard drive, did the drive letter of the external hard drive change?
Please review, consider, and supply more details and results. Any questions, please do not hesitate to ask.
Hope im ok picking up on this too....I'm having the same issue in Windows 10 due to a reinstall of Premiere Elements. I just dont get a request to find the files. Just the media offline message. If i keep trying I get a message about the files not being supported due to not having the correct codec? I do have Quicktime installed so run out of ideas??
Clean out media cache in the preferences.
Rename topfolder the pic are in and try again.