You can use this chart to adjust your screen. To get the best results adjust the contast to the highest setting first then adjust the brightness until you can see a gradual difference between the swatches 0 being white and 100 being black. If you are unable to adjust to a satifactory level its worth checking your monitor has a colour temperature setting, adjusting this noramally to around 6500k to 7000k is usually best.

Calibration Chart, Click To View Larger