When logged in as "linaro" you can reset the root password with the following command
sudo password
You will then be able
From the console you can disable X at startup by issuing the following command.
sudo mv /etc/init/lightdm.conf /etc/init/lightdm.conf.disabled
And then reboot the
To boot with PXE you must first enable the network cards BIOS within your system BIOS and then when booting