Can't adjust the brightness on a Toshiba C665 laptop

Try this:

1. Open a terminal (Ctrl + Alt + T).
2. Then type sudo nano /etc/default/grub. It will ask for your password. Type it in.
3. Around the 11th line, there will be something like: GRUB_CMDLINE_LINUX_DEFAULT="quiet splash". Change it to GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor"
4. Save the file by Ctrl+O followed by Ctrl+X. Then run sudo update-grub in the terminal.
5. Reboot and see if backlight adjustment works. If not, undo the changes you did above, by invoking the text editor as in steps 1 and 2.

Hope it helps.

Launch synaptic packet manager. Type in ACPI, check acpi 1.61 and acpitool 0.5.1-3,mark for installation,click apply and then reboot or restart.

Should work.

Worked for me on Toshiba satellite L450D-11V.