To unlock the bootloader switch of the phone. Then boot into bootloader/fastboot mode by holding volume down + power.

Plug the phone to your computer and make sure it could be found:

cd C:\Users\idefix\AppData\Local\Android\Sdk\platform-tools
fastboot devices

If it is found, continue:

fastboot oem unlock

Confirm on the phone using the volumn key and power button.

Reboot the phone with:

fastboot reboot

Now wait till the phone is completely booted again and restore your backup.