Hard Reset HTC Desire P

First method:

1. Turn the device on.
2. Go to Home screen, press Menu button , and then select Settings.
3. Select Storage then Factory data reset.
4. Select Reset phone, and afterwards Select Erase everything.
5. Now device will reboot itself.

Second method:

1. First step is removing battery for a few seconds.
2. Insert battery again.
3. Press and hold the Volume-down button, and then press and hold the Power button.
4. Wait for the three Android images to appear
5. When you will see Android images release the Power and Volume down buttons.
6. Press Volume down to select Factory reset (Clear storage), and then press the Power button. 

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