At my last reboot X started but blacked the screen. When logging into the system remotely all processes seem to be running just fine (e.g. Firefox is automatically started), so X is clearly running, but it is likely just a small switch that tells the screen to go black instead of showing the display.

I have tried removing xorg.conf and get the same result.

The system has an nVidia card and an Intel card. I have so far been using the Intel card, but as long as the drivers for the cards are free software I don't really care which card to use.

How can I get the display working again?

Xorg.0.log: https://gist.github.com/anonymous/94de1dab2894f183afbc

# lshw -C display
*-display UNCLAIMED     
   description: VGA compatible controller
   product: GK107M [GeForce GT 740M]
   vendor: NVIDIA Corporation
   physical id: 0
   bus info: pci@0000:01:00.0
   version: a1
   width: 64 bits
   clock: 33MHz
   capabilities: pm msi pciexpress vga_controller bus_master cap_list
   configuration: latency=0
   resources: memory:d2000000-d2ffffff memory:a0000000-afffffff memory:b0000000-b1ffffff ioport:4000(size=128) memory:b2000000-b207ffff
   description: VGA compatible controller
   product: 3rd Gen Core processor Graphics Controller
   vendor: Intel Corporation
   physical id: 2
   bus info: pci@0000:00:02.0
   version: 09
   width: 64 bits
   clock: 33MHz
   capabilities: msi pm vga_controller bus_master cap_list rom
   configuration: driver=i915 latency=0
   resources: irq:47 memory:d4000000-d43fffff memory:c0000000-cfffffff ioport:5000(size=64)

In /etc/default/grub I changed this:

GRUB_CMDLINE_LINUX_DEFAULT="text nomodeset acpi_backlight=legacy"



update-grub, reboot, and start mdm by hand:

/etc/init.d/mdm start

No idea why the backlight should suddenly break.

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