When i press brightness key little faster the screen turns black(when graphic driver is not installed) or corrupted(when ati driver is used) and i have to forcefully restart again.This happens even with software brightness settings.I have to reduce brightness because brightness is set to maximum every time i logout/restart.
NOTE:I always use my laptop with ac adapter
Update: I have removed 12.04 and installed 13.04 and I faced same problem, I added "acpi_backlight=vendor" option and the brightness across the the sessions is saved. But the screen is still becoming garbled and forcing me to restart again, Here is the snapshot of my laptop screen.
UPDATE: I have installed Manjaro Linux, to test for this problem, I have faced the same problem again. Seems like this a kernel level Problem.(I am pretty much screwed with any Linux Distro). Does anyone know a kernel, which does not have this problem. I will start testing out kernels from today.