[PC]Left 4 Dead brightness level won't save!

I installed left 4 dead almost 2 months now and i tried changing the brightness level to what is recommended to see the three lines (a more higher level) and played a level. I was satisfied until i have to rest. then when i run left 4 dead again it resets to default brightness again! Though its not a big deal, i'm getting real tired in always changing the brightness level. is there anyway to fix this brightness-doesnt-save problem? thanx.


My rig:
Windows XP Professional (SP3)
Asus P4P-800se
Pentium R IV 3.20 ghz (dual cpu)
Powercolor ATI HD 3850 AGP 512mb
1024 mb Ram
500-watt power supply

I tried but the steam cloud option seems unselectable. like it doesnt have description and nothing happens when i clicked it. Is there some way to just delete configurations file and start another one? like in the registry or the directory itself?