In order to hard reset a HTC Touch Diamond, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
HTC Touch Diamond device will be brought back to the default configuration of a brand new device.
1. Start by holding the Volume Down and Enter buttons.
2. Now pick up the stylus and put it in the hole placed on the lower right corner of the device.
3. The phone will now reset and restart with its factory settings turned on.