"Media Offline" usually means that the files it's looking for have been moved, deleted or perhaps stored on an external drive that has been disconnected such as a USB drive. If they were moved, you can point to the new location and everything should go smoothly after that. If that doesn't help fix your problem, provide some additional information such as how many hard drives your system has (internal or external).
I've never seen the software corrupt a video file however so that seems unlikely.
Hope that helps
This is not a programmed reply. I am not Adobe, but I am a real person who with past and current hands on experience with Premiere Elements troubleshooting. But, history cannot replace a here and now answer and success for you. So, if you are willing, let us try to resolve your Premiere Elements issues. The answers will be in the details...
1. What version of Premiere Elements are you using and on what computer operating system is it running?
2. Are you aware that you cannot move, delete, or rename the files that you import in Premiere Elements project after you have saved closed the project?
If you do, you will be greeted with "Where is the file....?" messages. Are you getting these? Remember, what you import into Premiere Elements are copies of the originals on the computer hard drive. And, the project needs to be able to trace back to those originals where they were when they were first imported in the project.
3. All that being said and being in order, there are other scenarios for what you have run into. Where do you have the project's source media stored - an external hard drive that you may or may not be plugging in or out as needed? If you are using an external hard drive for our source media storage, do you see the drive letter of the external hard drive changing spontaneously from time to time? If using a Windows computer, is that external hard drive formatted NTFS or FAT32?
4. Even though your project is having problems with its source media, can you actually see the files in the location where "they should be" on the hard drive?
Since the project has only copies of the originals, the program is not going to damage your originals.
Your answers to the above will help us to suggest a troubleshooting strategy to resolve your issues. But, details, please.