The reboot to know based on the OS

In case of technical failure of your smartphone, you need to restart force. In general, this manipulation is sufficient to correct many problems. 
As a phone is not like another, manipulations to perform a " reboot "are often different.

Here's a list that should help you out.

You have an iPhone running iOS?
You must press simultaneously on the Sleep / Wake and Home buttons of your iPhone. Then wait until your phone is off. Thereof restart soon after.

See This : This is a what looks like a HTC One (M8) Android 5.0 Lollipop

With a Nokia Lumia Windows Phone?
Press and simultaneously on low volume and power buttons. Vibration will occur after about ten seconds. Your smartphone will restart automatically.

If you Lumia 925, 1020 or 1520, you just simply press and hold the On / Off button.

With a Sony Xperia Android?
You must press simultaneously the buttons on / off and volume up for 8 seconds. Your phone will restart thereafter.

You have an HTC One Android?
Simply hold the On / Off button for more than 10 seconds.

You have a Samsung Galaxy Android?
Simultaneously press the Home key, low volume and on / off. This operation will require two hands but will allow you to reboot your smartphone.

With a BlackBerry BlackBerry OS?
You must press the Alt, Shift and Del and wait for your phone reboots.

You now know how to react in case of failure of your smartphone!