Tried Putting My Game on an External Hard Drive, Now I Can't Play

So I got an external hard drive to save my Sims game onto because my PC is, admittedly, a little old, and has some technical issues, and I just wanted to store my saves and custom content somewhere just in case my computer decided to dip one day. I downloaded everything onto it, I ejected the hard drive through Windows first, and got a pop-up telling me I can remove it safely, and now when I try to open my game it says the files are corrupt and I can't play. If I lost my mods and saves I'll be absolutely devastated. What can I do???