Power Button issue!! Please help

Hi All,

My mobile is N7000. Suddenly the power button is not working as expected!!
When pressing it the power off screen appeared instead of locking the screen!! If I did nothing to this power off screen the mobile will automatically restart!!
I pressed on it the normal press (the short one) to lock the screen but it's not doing so!!
I have formatted the device all of it and still nothing is working!!

I am in Jelly bean official rom.
Can any one help me please?

Thanks