Had problem on Lenovo W520 with Kubuntu 14.04 to get external VGA AND LVDS 
working. 
With Optimus no chance. 
Had to switch to discrete graphics in Bios.
Nvidia drivers nogo.
Switched to Nouveau i.e. reinstalled the driver.
But than had problem with brightness on LVDS.
Finally figured out working boot params:

GRUB_CMDLINE_LINUX_DEFAULT="agp=off quiet splash acpi_osi=linux
thinkpad-acpi.brightness_enable=1 nox2apic"

Other settings like recommended here
https://wiki.ubuntu.com/Kernel/Debugging/Backlight did not work.

Works for now. Will check next on docking station.

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https://bugs.launchpad.net/bugs/776999

Title:
  [Lenovo W520] laptop freezes on ACPI-related actions

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