Laptop brightness adjusting itself

[Jaa-Yoo]

I have a dell 1525 laptop with a new installation of windows 7. i have a problem with it continually adjusting the brightness of the screen all on its own. i would open the power options to find the slider lowered on its own after i moved it up to full. ive disabled every feature that i can think of (or google up) that would automatically adjust the screen brightness. i thought it may have been this generic power adapter, but i noticed something peculiar. let me try to explain...
if brightness is on a scale of 1 to 10 and i set it at 10, it will jump between 3 and 10, very annoying. but if i set it to 1, it will jump between 1 and 3. if i set it to 3, it doesnt move and the brightness stays set. its almost as if it wants to be set to 3 all the time.
any suggestions?

 

[Canon]

Turn off the ambient light sensor if your laptop has one. Usually it can be done with fm+an f key but some machines let you disable it in the bios as well.

 

[Bahamut]

Look at the cursor keys on that Dell, the Left cursor key should have the word Auto on it and a circle with dots on it (like a pictogram of a star/sun). If you hold the Fn (Function) key and then tap that Left cursor key it should turn the ALS (Ambient Light Sensor) on or off. If it's on, it'll obviously try to adjust to ambient lighting conditions (DOH!!!) but, with it off, you should be able to then adjust the brightness with the Fn + cursor Up or Down and it'll "stick" from that point on.

Even if you disable it in the BIOS, that Fn+Left cursor combo will turn it back on, and sometimes it happens with an errant keystroke by accident...