I dont have this phone. But i can say first u have to flash a ruu. I only find 1.08 ruu for europe. Then you change ur cid to HTC__001 via fastboot. Command is fastboot oem writecid HTC__001 . Then reboot phone check software updates and u will go...
a56dj_pro_uhl europe 1.16.401.21 RUU link: http://download1594.mediafire.com/125rnlxwlg3g/il3x4907cejobss/2PYAIMG_A56DJ_PRO_UHL_M60_SENSE80GP_HTC_Europe_1.16.401.21_Radio_0.A56DJPV1P22.6400.1208.A56U_release_492698_signed.zip.rar
password is www...
Download this file. Copy it to your ext sdcard and rename it to 0PJAIMG.zip
Connect your pho...
You have to flash RUU at download mode. Try to download rom.zip for att and flash it via download mode
yes this wipe everything.