I have a jailbroken iPhone 4, and today it randomly turned off (I know for a fact that the battery was not low). I tried using redsn0w to boot, but it didn't recognize the iPhone. The iPhone just stuck on the apple logo. I then tried putting the phone into recovery mode with iTunes, but when I hold down the sleep/home buttons, the apple logo just disappears, then reappears a couple seconds later. Pretty much, I'm stuck on the apple logo and not even able to get the phone into DFU mode or recovery mode. HELP!