Can you remove both of the acpi_backlight=vendor parameters from grub and reboot the computer? This time post back the results of:
...and the links to the following two log files:
You also mentioned that you tried to install the nvidia driver and that it didn't work. How did you try to install it? Was it through the additional drivers tab via:
...(or Ubuntu Software Centre, select Edit->Software Sources and on the Additional Drivers tab)?