Here's how to hard reset the HTC Desire Z with step by step instructions to clear all data and restore it back its original settings.
Note: A result of this procedure will delete all data stored from the HTC Desire Z. The data stored on the microSD memory card may or may not be deleted . We advice to back up all of important personal data before proceeding.
Resetting through Menu Settings
1. From the main home screen, select menu
2. Select Settings, then Privacy
3. Select Factory data reset
4. Select Reset phone
5. Enter the password if prompted, then select Erase everything to continue
If the HTC Desire Z is frozen amd can't access the menu settings
1. If the device is frozen,turn the phone's power off. remove the battery out and reinsert it in back again
2. Press and Hold the Volume Down button
3. Press and hold the Power button until the device turns on
4. A menu will then appear that let you choose for Fastbook, Recovery, Clear Storage, and Simlock
5. Select Clear Storage by pressing the Volume Down button
6. Press and then release the Power button
7. Then confirm, press Volume Up for YES and press Volume Down for NO
Once the the wipe completes, the phone will reboot to its factory default state settings. All data stored including third-party applications has been deleted from the HTC Desire Z. You need to reinstall third-party application again.