How to hard reset HTC Windows Phone 7

Hard reset your Windows Phone 7 using software method

This method will only work if you are able to boot your Windows Phone 7 and get to the home screen.
Tap start screen > about phone > reset your phone
Just in case you are not able to boot your WP7 handset you can try hard reset using the phone buttons.

How to hard reset HTC Windows Phone 7 handset using phone buttons

This method applies to all the HTC phones (HTC HD7, HTC 7 Trophy, HTC 7 Mozart) running the Windows Phone 7 OS.
If you can turn off the phone do it. For unresponsive or frozen phone, remove the battery and put it back again after few seconds.
1. Press Volume up button and hold then press Volume Down button and hold and then press the power button (briefly) to switch the phone on.
2. Keep holding the volume up and volume down buttons until you see a reset screen option.
3. Now follow the instructions that will show up on your mobile screen to factory reset your phone.