dudes !!
i've been trying to enter DFU mode for months now.
my Power Button is completely out !
today i opened up my iPhone 3g just to see what's inside and when i closed it up, i was touching it and i accidentally pressed the screen at the earpiece (the thing where you hear people talking to you) and it locked !
i thought 1 minute has passed but i tried again and it worked !
it worked when i tried to turn it off, it worked when i tried to turn it on AND it worked when i tried to enter DFU mode !
i just wanted to share, maybe it'll help someone out !