What happens if you start over from scratch, Import that project and DON'T hit stop?
It looks like a folder was moved or re-named. Look for the path to the missing file by scrolling right in the Project Panel and then look for that folder. If the folder or the assets cannot be found then search your system for the files. If the files are where they are supposed to be then please let us know and you still have the problem or cannot replace one footage item and have the rest appear please let us know.