Hey today I was just using my iPhone and it randomly shut off and wouldn't turn back on. I noticed before it shut off that it was searching for service for some weird reason? Anyways, everytime i try to turn it on it boots up to the apple logo and immediately shuts off afterwards. I put it into restore mode with iTunes but I can't get it to restore - it just keeps giving me error 21. I've done all the error 21 fixes I could find on google to no avail. Does anybody have any knowledge about this that can help me fix it? It would be appreciated, thanks!