Too bright screen?

I need to sell/buy something in my private store. my friend needs to use the computer so I decided to minimize L2 and let my friend use my computer to do his IT Business. The problem is whenever I minimize L2, the screen gets brighter. :confused:



anyone has an idea? the brightness makes your eyes hurt for prolonged staring.:confused:



but when i restore L2 the game has normal brightness.



System:

Intel i7-3630 @ 2.4 GHz

Win7 64-bit

8GB RAM

NVIDIA GeForce GT 645M