It sounds like someone has adjusted the video settings in your graphics card control panel.
It all depends on what videocard do you have as to how to correct it.
If it's Nvidia, right click on your desktop and click on the "Nvidia Control Panel". At the top of thee page choose "Advansed settings". In the Video & Television task section choose "Adjust video color settings" and then click on the "RGB Gamma" tab. See if the use RGB gamma box is checked and if so, uncheck it. Click on the "Correction" tab and choose "Do not use color temperature correction".
If it's ATI, there should be a choice to change the settings that is somewhat similar.
After the problem is corrected, you can tweak the settings a little to get your video to where you like it.
