The normal process to restart is to hold down the Sleep/Wake button on the top of the phone and slide the slider to restart your iPhone. The next step if your iPhone won’t turn on, is to restart it. You could even try charging a friend’s phone to see if there is a problem with your charger. Inspect your cable and adapter for any obvious signs of damage that could be causing a problem, such as a frayed cord.
If your phone still won’t turn on, try using a different USB cable and power adapter and check the jack (where the charger plugs into the phone) in case that’s where the problem lies. You can leave your phone connected for up to an hour before deciding it is indeed not working (as recommended by Apple). It usually comes up within a few minutes if there is no issue. Plug your phone in and wait to see if the charging screen comes up. This seems like an obvious step, but may save a lot of trouble in the long run. If your iPhone won’t turn on, the first step is to plug it in to charge. Follow these steps to troubleshoot this problem. When you find that your iPhone won’t turn on or charge you will need to determine if there is a software or hardware problem. 7 Tips to Try When your Apple iPhone is Dead.