Why my display brightness decreases automatically
my display brightness automatically decreases almost to 0. when i open my pc or wake up it from sleep but after some minutes it looks fine.
I found this article
I don't know how much applies as I don't know which version of windows your using (this guide is for 8.1), but essentially I think your looking for the "Adjust my screen brightness automatically", or something similar.
Let me know if this helps.