Technically it's normal when some gadgets like smartphone occasionally malfunction and iPhones is not an exceptional and one of the most problem iPhone usual have is that it fails to power on occasionally that might force you to take the smartphone to technicians but trust me most of those problems is what you can easily do by yourself without taking your phone to any technician.
Why iPhone won't turn ON
As I said early an iPhone can malfunction anytime but this problem often happens when you allowed your smartphone battery to dry the phone turned off by itself then after charging it you might face some difficulties turning it on again but there is a solution to such problem, don't panic yet.
Some technicians might use this opportunity to extract some money from you knowing fully well that nothing was wrong with your iPhone but such thing will never happen again after reading this post.
What to do when an iPhone failed to power On or won't turn On
We have come to the most important part of the reason why you are here and we are going to explore many options on how to force an iPhone to turn on when it fails
If your iPhone is not having any other serious issue then be rest assured that you will learn how to turn it on before leaving this page
To forcefully turn your iPhone on simply Hold down the home button key and then plug the USB lead into the back of your computer at the same time and see what happens, you will be surprised to see that your phone is already on.
Most of the iPhone will not be able to work at when it doesn't have enough power to work and if it shows you red sign that the battery is low, make sure you charge it at once but If the iPhone’s battery is completely drained you might not be able to see the battery recharge image for few minutes and it is normal if the screen remains blank when you plug it in you just have to wait a while to see if the icon appears.
If your iPhone is still not ON yet then there is one last thing to try before taking your phone to Apple store which is using DFU modus method.
DFU simply means (Drainage Fixture Unit) and a means of putting your iPhone into a special mode that enables it to interface with iTunes but does not load the iPhone operating system or boot loader though.
To put your iPhone in DFU modus start iTunes and plug-in your iPhone even if it is turned off or when it only shows the apple logo and then press down the power button for 3 seconds and now press the home button while still holding the power button.
Keep holding both buttons simultaneous for at least 15 seconds and then release the power button and continue holding the home button for about 30 seconds and your iPhone will be detected by iTunes.
You might be asked to restore your smartphone to the factory defaults settings which will finally restore your iPhone to its functional state.
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I hope this guide will help you restore your iPhone without spending any additional cost but if you followed all the instructions correctly and it still fails to work for you then you might need to visit apple store for more help.
Feel free to ask more question if you have any and I will be glad to help