I can no longer adjust the brightness of my laptop screen, it's stuck at the lowest.

In Linux, the brightness adjustment keys (Fn + F4/F5) still work, since a brightness popup shows and the meter bar changes, but it does this in a strange way. Starting at 100%, each successive press of the "lower brightness" button moves the bar to:

• 67%
• 50%
• 0%
• 26%
• 12%

Or another random pattern like that. The problem is not Linux however, since I can't change the brightness from Windows (7) either.

Where do I even begin to look? Since the problem does not seem be OS-specific, I've searched in the BIOS, but it has no option like that.

How did this happen? I think it's been this way since when I lowered the brightness to 0%, then pressed the "lower brightness" key again. Not sure about that though.