I changed my PC, and took a copy of all photos to an external drive. Now, when I want to save them to my new PC, it does not succeed - next time I open my Elements, there is a ?-mark, and the program can't find the photo unless I connect the external drive again. How can I save all photos to my new PC?
What version of Premiere Elements are you using and on what computer operating system is it running. For now I will assume this involves a media reconnect in Premiere Elements and not the Elements Organizer.
When you import media into a Premiere Elements project, all you get in the project are copies of the originals that are at their hard drive save location. But, the project needs to trace back to the originals at the hard drive save location where they were when they were first imported into the project.
You should not have any problems when importing media from their current location when you open new projects.
How many saved closed projects do you have that were created before you switched the location of the source media of the project. (Remember, you will run into this problem if, after you save close the project, you move, delete, or rename its files/folders.) The "Where is the file....?" messages are good choices for the media reconnects, but... Let us know how many saved closed reopened projects are involved. Also, if the setup on the other computer still exists, it might be a consideration to archive the projects there and transfer the Copied Folder from the archive process to the new computer.
If instead this is a Photoshop Elements Elements Organizer based issue, please let us know.