hi, a friend of mine, brought his i4, it keeps on restarting up to apple logo. when he brought it, it was dead and when i put it into computer shows apple logo and goes blank and shows it again and keeps on ... its annoying. I dont know what he did. He told it was on 5.1 and jb'd tethered. i have tried several things but still keeps on restarting. I can put it into DFU mode. but he needs to fix it without restoring if possible. Is it possible to fix it? or is it battery issue?? Need your help Please!!!