Premiere Elements 13: Footage not being seen in edit

Hello,

I am editing a wedding video. After completing the edit and being happy. I took a few days off. After a few days off I opened my project to find the screen that pops up and normally asks you 'where clip 36' is etc. I pressed Skip all as the box did not give me the option to find the footage.

I could seem y timeline and all the edits in place. Half the film was there with the footage and the other half was there in its edit position but without the footage.

I restarted the project hoping to be able to be given the option to find the footage in the box which normally says 'where is clip 36' etc but again the box did not give me that option so I had to press skip all again. Then I had to write down all the clip footage names. Find it on computer re-import into project assets and then line it all up again above the edited footage to re-edit.

My QUESTION is WHY has this happened and why is my adobe premeire elements a) not able to sync the footage to the edit I've already done?