Iphone 4 Turned off and wont turn on

Try connecting it to a charger

Did you press and hold the Sleep/Wake button and the Home button together for at least ten seconds?

Did you check the LCI http://support.apple.com/kb/HT3302

Did you try to enter recovery mode?

Disconnect iPhone from computer
Launch iTunes
Press + Hold Home + while holding the button connect iPhone to USB

Better take in for service

i have the Exactly same problem, luckily, after i tried to connect with computer and hold the Sleep/Wake button + the Home button together for at least ten seconds, it work.

HOWEVER, i am not sure that this is the handset problam or other, should i go to check/Maintenance??

any comment?

i exactly had the same problem 5 mins ago. i didn't know what to do. luckily, i have read this forum so i tried connecting it to the computer and held the home button+ sleep/wake button for at least 10sec and it went on.

I wonder if this is a problem of the headseat or something else?

My wife's iphone4 turned off spontaneously after she sent a message and it had 95% battery. Nothing we did turned the phone back on. After searching the net and looking at this forum I held the sleep/wake button and the home button together and it turned on... Amazing. Thanks to all those who have posted. Is this a recurrent issue though? Would definitely like to know if this is a handset- and/or OS-specific problem?

Thanks for the advice...tried it and it worked. ;))

Wow, thanks to this post! I knew to push the home+sleep button but i didnt know it had to be hooked up to the computer! Thanks! Hopefully this doesnt happen again..