Hello iesmat, welcome to iMore!
Hard reset the device (this does not delete anything, it's just a hard reboot).
Quickly press and let go of the volume up button.
Quickly press and let go of the volume down button.
Press and hold the power button until you see the Apple logo. You may or may not see the slider to power down the device.... don't let go, continue to hold the power button until you see the Apple logo. Allow the device to reboot.
Let us know if that helped.