Hard Reset HTC HD mini

First method:

1. First to do is power off your device.
   
2. Next step is press and hold Volume Up + Volume Down + Power button.
   
3. When you see warning message in your screen, then press Volume Up to confirm operation.
   
4. Now if you see information "Restore Completed", then press Volume Up.
5. After that wait to noramlly power on your device.
6. Good job!

Second method:

1. Turn on your phone.
   
2. Now from the Home screen go to Settings -> Security -> Factory Reset.
3. When is promted, then enter your password.
   *The default password is: 1234
4. Then confirm your choice, tap "Yes".
5. Success!

WARNING !
Hard Reset will erase all of your data
All described operations you are doing at your own risk.