Do the patches marked 0 and 10 in the grayscale appear to be the same? If they do then you need to calibrate your monitor black point. Do the patches marked 95 and 100 appear to be the same? If they do then you need to calibrate your monitor white point. If the patches have a color tint, you can correct problem by calibrating monitor gamma for each color channel individually.
Stand ten feet from your monitor and examine the above figure. If the smooth patch is darker or lighter than the background then you need to calibrate monitor gamma.
You can calibrate black and white points without any special software. To adjust monitor gamma, you'll need special software such as Adobe Gamma or QuickGamma. Adobe Gamma comes packaged with Photoshop and Photoshop Elements. QuickGamma is free software that can be downloaded from QuickGamma web site. The techique used in both cases is similar. Do not install QuickGamma if you already have Adobe Gamma.
It takes just a few minutes to make these a djustments. As a reward, you will view images on the web as they were designed to be viewed.
Be sure to set monitor color temperature to 6500° and color quality to at least 24-bit before calibrating. With 16-bit color there is not enough color depth to calibrate properly. Let your monitor warm-up for at least 15 minutes before calibration.