You might try using redsn0w's fix recovery and see if it helps. You basically put it in pwned dfu mode and it runs some jailbreak stuff on it to get a phone booting again.
I spent hours running around with the phone in various states the other day and this fixed it for me (although not exactly the same as yours, it couldn't hurt) Also try using redsn0w to preserve the baseband as well, either by reloading this one from pwnd dfu mode or creating one with redsn0w itself and loading it.