Okay, I jailbroke my friend's iphone 3G in tethered via redsn0w 0.9.8b3 with the firmware 4.2.1 (8C148) for the iphone 3G. Then, he encountered a situation in which he had to power down his phone. So when he came back to me to reboot in tethered mode, I tried to do a hard reset (sleep+home button), but It would't work. The apple logo just stays until it runs out of batteries. Occasionally the screen goes black and the apple logo pops back up. Anyone know the remedy to this? Thanks!