Just to make a check list : The Jolla phone is updated to the latest 34.3.A.0.228 or .238 firmware (Important to do first because after unlocking the boot loader, OTA won't work as easily) Developer menu is activated USB debugging is on 3rd party application are authorizsed OEM unlocking is authorized You have registered your IMEI on Sony's website You've obtained a long hexadecimal code in return from Sony Your phone was first shutdown Afterwards (wait 10 seconds at least), your phone was turned on in Fastboot mode (hold "volume up" while plugging the USB cable) the Xperia is in Fastboot mode (no message on the screen, the LED is blue instead of green At that moment you should run the fastboot command in your command shell (in cmd.exe) : fastboot.exe oem unlock 0x<hexadecimal code> Note that depending on how windows works, this might require admin rights (I have no idea, I use Linux. Maybe you'll get a UAC security prompt ? Or you need to "Run as..." cmd.exe to start the shell in admin mode ?)