How can I change the Gamma setting on my monitor?

For some reason the brightness/whiteness on my laptop's (Toshiba PC) monitor has increased. I tried to go onto the display and calibrate the color. I got to the option to change the gamma settings, and moved it all the way down to something that looked more like what it did before, and the screen doesn't change. But when i click on next all the way until i finish- everything is left unchanged. I don't know what to do. advice? Im having a really hard time seeing the scroll bar, and the names of songs etc on pandora are nearly impossible to read, like a white haze around everything. Help?!?!