What version of Premiere Elements are you using and on what computer operating system is it running?
How did you save your project and to where?
What was on that Timeline when you saved/closed this project....all photos or a mix of photos and videos or all videos?
What were the pixel dimensions of the photos and how many of them were there?
When you open this project which had photos before the save close, are you getting any messages such as "Where is the file....?"
If you start a new project and do the save close, when you re-open the project, are the photos there?
:Let us start here and then decide what next.
Looking forward to your follow up.