OKI, briefly tutorial:1:
You must visit bootloader unlock page: http://www.htcdev.com/bootloader
BUT! YOU LOST ALL OF THE CONTACT & APPS & PERSONAL SETTINGS. MAKE BACKUP!
Process all steps of unlocking procedure, it is good documented.
As result, you have device with fully functional bootloader.
2: Obtain UnlockRoot tool. Find a file, named unlockroot23-eng.exe, size 9479 kB. You may try visit the developer page http://www.unlockroot.com/