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I have followed the fix found here: Backlight Issue

However I can't use the sudo update-grub2 command as it errors with

/usr/sbin/grub-probe: error: cannot find a device for / (is /dev mounted?)

As this laptop's hard drive is shot, I can't install the OS. So I'm using a live usb & I have been able to get it to temporarily work in Terminal with

sudo setpci -s 00:02.0 F4.B=00

I'm new to Ubuntu, so if you know how to fix this please provide as much detail to what I would need to do.

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fist off buy a hard drive............

secondly i have the same issue with my emachines e525 ( acer )

heres what google magic found for me. i dont know if it works... it makes no sense to me but i thought id drop it here b4 i go try.

I wont be back so good luck lol

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Welcome to Ask Ubuntu! While this link may answer the question, it is better to include the essential parts of the answer here and provide the link for reference. – Peachy Sep 27 '12 at 7:33

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