lock problem

[kashilachu]

My phone don't lock when press on lock button 

[jawahaar]

you should have changed the setting for the power button

[ShahidBD]

If device's power button is fit to work and didn't changed its default action then go to your device Settings > Lock screen > "Smart Lock" then "Turn Off" all of unlock type here like On-body detection, Trusted places, Trusted devices. Then try.