Samsung Z2
Back up your user data and make sure battery charge is up to 70%1. At First Turn Off Your Device by pressing the power key.
2. Now Press and hold volume up + Home + Power key to turn on your cell phone.
3. After a few seconds show the android logo on-screen and release the power key. keep pressing volume + Home.
4. now show the android recovery menu on the screen and select the "wipe data/factory reset" Volume key to scroll and the Power key to confirm.
5. then select this "Yes -- delete all user data" again use the volume keys to scroll and confirm by pressing power key.
6. after finishing this whole process then select "Reboot system now " pressing the power key to confirm.
after confirming the waiting a few seconds devices will be automatically restarted and fix your problem.