well assuming you dint really steal it..
you can do a hard reset with the buttons....<
1. Press and hold the Camera, Volume Down, and Power buttons simultaneously.
2. Release Power when the phone vibrates, but continue to hold down Camera and Volume Down.
3. Release Camera and Volume Down when the Format prompt is displayed on screen.
4. Press WP7 Windows button.
5. Press WP7 Windows button again to confirm the hard reset.