Hard Reset CELKON WIN 400

First method:

Turn off your mobile phone by holding the Power key for a short while.
Afterwards press and hold together the Volume Down and Power button until you feel a vibration.
When you feel the vibration, immediately press and hold the Volume down button until you see a large exclamation mark.
Then press the following sequence of buttons: Volume Up - > Volume Down - > Power - > Volume Down.
Success! Tha hard reset has just been performed.