I just got my friends' iPhone and he claims he's broken. So I sent it to a repair centre and they told me the logic board was broken. However, when I try to recharge the iPhone by plugging it in the wall, the Apple logo appears and it seems to be booting just fine.
Only, when I pull out the plug, the phone immediately shuts down, although the battery indicated it's fully charged. So I think not that the motherboard is broken, but that there's some kind of battery issue. I've tried replacing the battery, but that didn't work out. Another interesting thing is that the phone keeps rebooting. After booting, it shows the "connect to iTunes" screen, but after 5 minutes it's back to rebooting.
Is it really the (connection to the battery on the) motherboard or can you think of something else?