How to remove a "Private Protection Password" on an ANDROID MT6592, please? I guess one of my kids activated this kind of password that suddently appeared on my YHAPPY UP620.

The USB mode is not available, so that my PC does not see my phone, and I can not flash it...

How can I solve this problem, please?
Oh! Its very simple. Try to press volume- &amp; power key at a time the will  display a factory reset settings and click on rest and your mobile will be unlocked.