Warning: This will remove ALL data on the phone (but not the MicroSD card).
To perform a hard reset, or factory reset, then there are a number of methods to try:
1) From the home screen, press Menu - Settings - Privacy - Factory data reset - Reset phone. It may ask for a password. Then select Erase everything
If the phone is totally unresponsive, even after a reboot, then try the following methods.
2) While the phone is turned off, press and hold the Volume Up and Volume Down buttons together. Then, while holding these, press and release the Power button (keep holding the volume buttons). The phone should turn on and a menu will appear. Press the Volume down button to navigate to the Recovery option. Press the Volume Up to select (if that doesn't work, use the Power button to select). A yellow triangle and an Android logo will appear. Press the Volume Down and Volume Up button together and a recovery menu should appear. Use the Volume buttons to move to the Wipe data/Factory reset option and then press Power to select. Again, use the Volume Down key to choose Yes and press the Power button again to select.
3) While the phone is turned off, press and hold the Volume Down button. Then, while holding, press and release the Power button. A menu should appear. Use the Volume down key to go to Clear Storage. Use the Power button to select the option. Then when asked to confirm, press Volume Up for Yes.
4) While the phone is off, press and hold down Volume Up + Home + Power buttons at the same time. Then release the buttons when you see the Logo. Use the Volume Down button to go down and the Home or Power key to select. Choose the Wipe data/Factory reset option. Then Select Yes to delete all user data. Then choose to reboot the phone.
5) A final method is to enter the code into your phone's dialer: *2767*3855# This method will not give you an option to reverse the process, so be careful! This method will only work if you can boot into your phone.