What if you found your iPhone screen cold,dark and no response when you press home button? Your friends might say "Do the hard reset. Press power and home button for at least 6-10 seconds".
No luck! I see the apple logo, but in seconds it's back to the deep sleep. What should I do?
First, don't be panic. Your iPhone is completely OK. It might be caught in the bootstrap error or might be crashed because you just installed a new app. Calm down and just follow the step by step instruction.
Before you start, it is recommend to have your computer freshly started. Sometimes USB in idle computer might fail to 'awake' which can cause connection or device recognition error.
Run iTunes in your PC or MAC. Make sure it's completely running and not in the loading or upgrade process. Connect your iPhone's cable and wait for few seconds before proceeding to the next step.
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PRESS and HOLD power button (on the top) and home button (in the front) in the same time for at least 6-10 seconds. Theoretically should be 10 seconds, but it's all trial and error until you get the right timing.
Once you see the connection image as shown in the picture, release the power button, BUT KEEP HOLDING the home button.
In seconds, you will hear beeps from your PC or MAC, follow by iTunes showing displaying request to restore. Release the home button and follow the recovery process.