What version of Premiere Elements are you using and on what computer operating system is it running?
If you opened a previously saved closed project and were greeted by a colorful media offline display and "Where is the file.....?" messages, there are at least two possibilities.
1. You have move, deleted, or renamed files and folders that you imported into the project after you saved closed the project.
When you import media into the the project, all you get in the project are copies of the originals which are at a hard drive save location. However, the project needs to
trace back to those originals at the location where they were when you first imported them into the project. You can use the "Where is the file....?" messages to reconnect
your source media to the project. Can be time consuming and a nuisance.
2. If you stored the project's source media on an external hard drive and that drive changed drive letter for some reason, this would create a media disconnect situation.
Correct the drive situation if this applies to you.
Please review and consider and supply more details. We can discuss this and other related matters (such as use of the Project Archiver) depending on your details.