Often when you install different Ubuntu versions on your Lenovo G780 the screen is going blank after reboot.
Nothing seems to work when you try to fix it.
Try to use the build in hardware feature of screenlight adjustment.
Press the Fn button while pressing the “up” button several times. If everything else works normally, your screen should slowly turn more bright and show the login screen.
‘Quick fix‘ it surely is, but it took some headache to figure this one out 😉
Tried this with versions 12.10 / 13.04 / 13.10 (beta) /13.10