Hmm try changing your rendering system. Maybe you have a corrupt file which is preventing you from entering the game. Also it could be your graphics, just try changing it to low, and see if that helps. If none of the tips work just go to this thread http://feral-heart.com/smf/index.php?topic=10423.0 It explains lots of things that can help you.How do I change the rendering system?
On the main menu, go to options and then video and just click the one that isn't highlighted. If there is no other option, go to the .ogre file in your FeralHeart folder and change it there.
They should still work, yes. Be sure that you save any files that are necessary for your maps to work properly, however, which include the object files, sky files, basically any files that make up your maps. Make sure that these files/folders are saved outside of the Feral Heart folder so that when deleting, you don't accidentally delete your backups. Your characters will stay as they are since they are connected to your account, and not your actual game files (unless presets, add-on markings are used, in which you would also need to back these up.)
If I delete the folder after re-installing, and then placing my maps, presets and textures + some of my settings back in my characters should in tact and my maps should work?