Are you trying to open a project file from an older version of Premiere Elements in Premiere Elements 13?
Or, have you done a project in Premiere Elements 13, saved closed it, and now reopen it to find a lot of colorful displays
and "Where is the file _____?" messages?
Major question...forget about the project for the moment...if you go to the computer hard drive, can you spot the files
that the project is telling you are missing?
After any of these project files were saved closed, did you move, delete, or rename files and folders that went into the project?
Let us start here, and then we can decide what next and then go into a lot more details to get your project's source
media reconnect to the project.
Never hesitate to ask questions and ask for clarification.