Woke up one morning and my iPhone 4 was dead, I tried holding in the power button, charged the phone and nothing happened, did not even make a sound or showed the apple logo. Although the previous night the battery was still 77% charged, but the phone just was dead, luckily I managed to get it on again
- Hold the Power Button and the Home Button together for between 15 and 30 seconds, you notice the Apple logo will appear and the iPhone 4 will switch on.
- If the iPhone4 keeps on going off, try the above solution again and then Go to Settings->Reset->Reset All Settings (NOTE: This will reset all your settings to factory defaults, but won’t delete any data, I suggest before doing anything you are unsure about backup your iPhone 4)
- The last thing to try before going to the Apple Store is to do a Factory Restore from ITunes