It will remove all the data ,contacts and apps that you installed
1. With the phone off, hold the Volume Down button and press and release the Power button.
2. You'll boot into the menu you see above with the little skateboard guys. Select Clear Storage from the list by pressing the Volume Down button.
3. Press the Power button, and confirm by pressing Volume Up.
4. Sit back while your phone reboots in its virgin state.
Nexus One Restore Factory Hard Reset Format Phone.So lets start the Nexus One Restore Factory, Nexus One Hard Reset.Turn Off the mobile phone for few mints.Nexus One Remove Pattern Lock.
Restore Hard reset will set your phone in origional factorry settings. It will remove all the data and apps that you installed. Your contacts will be removed and you have to add them again.