You might want to try right clicking on the desktop, go to Properties, then Settings Tab. Click on the Advanced button. Do you see a tab with your video card make and/or model on it? If so, go to that tab. Some video card drivers have a special area for additional settings where you can adjust brightness, gamma, etc. If you don't see the tab, check the Troubleshoot tab, and see that the Hardware accelleration slider is set all the way to the right (full). You might have to reboot to get the changes to take effect. Then you should be able to adjust your settings.
However, some drivers will not allow you to do this. Thus, you might have to either roll back the drivers as suggested or adjust your monitor (not really recommended).