This may bring up some nightmarish feelings if you've ever had to deal with Sprint's Customer Service but have you tried doing a hard reset on your phone? I had that happen to me once where no home launching app would work after trying to root my phone for the first time using a rooting from the phone app. In my case though even restarting the phone would not help me so I had to go into the status bar and fortunately I had an app that lived in the status bar and was able to get to the market and reinstall Go Launcher EX which gave me enough time to go into the settings menu and do a factory reset. That's the only way I was able to get any and all of my home launchers to work. I realize doing a factory reset is a real pain but its better than having to constantly dealing with a black screen and a useless phone.
I don't know if you're rooted but if not you might want to give AirDroid a look at to do a pretty much full back up for those just in case factory reset times. I don't know for sure if it actually does a full back up like a nandroid back up but I know I'm able to back up not only all my apps and files to my computer wirelessly but also system files and other apps you cannot normally back up, even the dreaded bloatware. Fantastic app and its free. It has saved me at least a few headaches where I've had to do a factory reset. Hope this helps.
Jim
Edit: Sorry, I guess I read your message too fast. I saw after replying that you've done a hard reset. The only thing I can think is if you want I can send you TwLauncher.apk and see if that gets it working again. Oh, and that's what I mean about using AirDroid for backing up my phone. In one of my folders called "Apps_System" the TwLauncher.apk file is backed up to my computer. Let me know if you want to try using a fresh TouchWiz file and see if that helps you get back on track. I can send it through e-mail or if you can tell me how to find my "DropBox" link I can put it in there and you can just grab it out of there. Take care.
