This may torture you, but you're going to have to delete all of your custom maps and meshes and reinstall FeralHeart. Delete your FH folder entirely, re-download FH (when it tells you the setup files are corrupt, it means that the installer didn't download completely. This is just a glitch that I've actually experienced myself.) You can try the torrent if the normal download doesn't work for you, but first you'll need utorrent which you can get here:
http://www.utorrent.comWhat this will do is simply give you a mostly clean sheet to work with. You might also try updating your graphics card and checking which rendering subsystem works better for you (options>video>rendering subsystem>openGL or direct3D9).
Good luck, and next time don't let your friend mess with your files. xD