Did you move your project file or the video files? They shouldn't just randomly break.
One of my coworkers had a similar issue because he would copy a project file off of a network drive into his working folder and (obviously) all of the file paths would break because they were relative. He has since been coached on proper workflow.
So long as the folder structure hasn't changed for your video files, once you relink one, After Effects should find the rest. In the future, if you're planning to move stuff around, you might look into the Collect Files feature.