Windows Phone 7

Set your password!

  1. On Start, flick left to the App List
  2. Click Settings
  3. Tap Lock + Wallpaper
  4. To set up a password for the first time, turn on Password, enter your new password in the New password text box, and then reenter it in the Confirm password text box
  5. If your phone already has a password and you want to change it, tap Change password, and then enter your phone’s current password in the Current password text box before entering your new password.
  6. Set a time limit for screen time out (the amount of idle time before your phone locks itself) by tapping Screen times out after and then selecting the time length you want.

http://www.microsoft.com/windowsphone/en-us/howto/wp7/basics/lock-screens-faq.aspx

 

Reset your Windows Phone:

If you wish to preserve your settings and content on your windows phone, we recommend you Back Up your device before you reset it.

http://www.windowsphone.com/en-us/how-to/wp8/basics/reset-my-phone