Reset Lubuntu's Resolution

sudo service lightdm stop
sudo Xorg -configure
sudo mv xorg.conf.new /etc/X11/xorg.conf
sudo vi /etc/X11/xorg.conf

sudo service lightdm start

https://help.ubuntu.com/community/Lubuntu/Monitor_or_Screens#Screen_resolution_is_wrong.2C_no_matter_what_I_do