Mainegeek pretty much has it all, only thing i am gonna add is that you can try adjusting all the other adjustments after you degausse first. Of course, you will find adjustment buttons for a ton of settings, adjust them all to your liking after degaussing and then degauss again when you have adjusted all the settings.
If that doesnt clear things up then we have to look at the video card drivers, video card, and monitor as probable sources of the problem, not always in that order.
After that it would be a longshot, windows os error? (doubt it), power supply (dont think so), motherboard - possibly, just not likely.
Interference? For sure, move all cell phones, speakers, anything magnetic out of range, that goes for wireless telephones too!
Good advice + great people = tek-tips