One common issue is re-arranging which folder the images are stored in. If you switched drives, then the folder path might be the same, but now the photos may be on E:\ instead of D:\
If you are CERTAIN that all of your filenames are unique, then you can use Lists > Media Galley > [Tools] > Fix broken media links to resolve your problem
If, however, ANY of your files have the same name as another (which could happen in my old file naming scheme, but not in my current one) then you may be able to use Search > Search and Replace > Multimedia filenames. In my example above, you would enter Search for > D:\ and Replace with > E:\
But, unfortunately, there are other ways to mess up media links. Only a close inspection in Lists > Media Gallery or in the Media Album for a person, fact, citation or source can reveal the actual problem, and lead to a solution.