After installing Ubuntu 13.04 as the main OS on my HP Pavilion dv7 laptop, I noticed that I could not change the screen brightness using the f2 and f3 brightness keys.
I found an [article on ask ubuntu](http://askubuntu.com/questions/162409 /brightness-not-working-on-an-hp-pavilion-dv6-with-a-ati-radeon-hd6770m) that solved the issue for me.
Here is a summary of the steps:
$ sudo cp /etc/default/grub /etc/default/grub.date +%F`
$ sudo vi /etc/default/grub
change the string associated with the variable GRUB_CMDLINE_LINUX_DEFAULT from “quiet splash” to “quiet splash acpi_backlight=vendor”
$ sudo update-grub
$ sudo reboot
`
This worked for me without an issue. If it still does not work, the article mentions additional steps that you may try.