This is interesting and may be due to an incompatibility between the nvidia driver and the sony video ACPI platform driver.
Originally Posted by khosro
This is only a suggestion and may not work but it's worth a try.
Reinstall the nvidia driver.
Open a terminal and type
Look for the lines that say
sudo nano /etc/default/grub
and change to
Run and reboot your PC.
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=video"
What we are trying to do here is use the standard ACPI video.ko driver and not sonys platform driver.
I don't know if this will work but it's worth the 5 minutes to give it a go.