1. The device can still enter FASTBOOT
2. You have the corresponding RUU
1. Enter FASTBOOT, and then connect to your computer (FASTBOOT USB will be shown)
2. Open command prompt in your computer
3. Relock your device by typing "fastboot oem lock" (you should know what is this if you HTC-unlock your phone before), the device will reboot.
4. Enter FASTBOOT again (you will see *** RELOCKED ***)
5. Apply the RUU
6. You device will be stocked
Note: The device must be relocked in order to apply the RUU.