I have a Gateway laptop just over a year old that will occasionally have a screen flicker that changes the brightness. It’s almost as if the power supply was unplugged and the system went into battery management reducing the brightness and then will return to bright. We move the computer around to bring full brightness back but I can’t say for sure what we do to make it return to normal.

I had the same problem and solved it as follows. Since there is an intelock that turns the monitor off when the laptop lid is down, or almost down, I guessed that perhaps that interlock, which must be somewhere in the lid's hinge, may be dirty. All I did was rapidly move the monitor back and forth. I moved it about 10-12", quickly, maybe 25 times. To my surprise, that did the trick! That was a month ago and the flicker hasn't returned.

Good luck. Hope it works for you, too.