Degaussing is the re alignment of the three beams at the back of your monitor (inside the monitor case of course). Sometimes, these three beams , consisting of a red, green, and blue light, get out of line and the make the screen appear over greeny, or dull red. Degaussing simply realigns these three beams.
If you have an onscreen display for your monitor, try finding the option, but if your monitor is old, it will not have onscreen display.
