You may not have given enough info to be sure the issue is a corrupt source. Is there anything else different about the 100 project files that won’t open compared to the others that will? Are they on a different drive? Do they use any of the same sources? Have any of either been moved or altered? Do all of your drives have enough available space for cache files, etc.? Did you have any crashes or other system issues either while working in AE or in general?
[Heather Crank] “If the problem is with a corrupt asset, how can I fix this problem?”
Usually, sources only become corrupt as a result of a specific event (i.e., a crash while files are being written to, etc.). So, it’s unusual for many sources to become corrupt at once (except in the scenario mentioned below). If the issue is a corrupt source, you have to somehow isolate the corrupt source(s). This is tedious if it’s a large project, but you can temporarily move all sources to a different location so that AE can’t find them when you open the project. Then, replace them one at a time until you come across one that causes AE to crash.
[Heather Crank] “Is it possible that all the files from the last month on both drives have become corrupt?”
It’s possible, but very unlikely for all files on two separate drives to become corrupt at the same time … unless something happened to both drives at the same time and it would be something that’s hard to miss (i.e., a system crash while files are being initially copied to both drives at the same time).
By the way, I’d suggest never working with files in AE that are located on a computer’s desktop since what’s on a computer’s desktop are usually shortcuts to files that are really on the system drive … personally, I think it’s a bad idea to store any data files on a system drive and always have at least one separate data drive.