I had the same problem and this helped me: First, don't hold in the power button, just push it. Then push it again and then hold it in. Hitting it that once was to make sure it was locked properly. Then you can hit the restart, reboot, help, etc, but that depends on the phone you have. You can also hold power and volume up button at the same time. If you use volume down for this technique, it will just take a screen shot and you will have to start all over. If you didn't lock it yet, download a screen pin with wallpaper app to replace the PIN with a brand new one. I hope this helped you! Thanks!