Need help with this weird problme

Hello everybody.
I recently bought a Dell SX2210 monitor and when i got it I was quite happy with it. After a week I started noticing some weird pixelation in my games. At the beginning I thought that something was wrong with my videocard so I updated my drivers and all that jazz but I still was getting the same problem, then I borrowed a monitor from a friend and the problem was gone!. The pixelation I'm getting is kinda weird cause I only seem to get it whenever there's movement from the images on the scren OR when i move my eyes across the monitor. If the picture is still then everything looks clean, but movement (mostly horizontal movement, which seems weirder) messes up the images and the pixelation begins to occur. The pixelation is very much noticeable under normal windows apps, but it's really annoying when i'm playing games or watching movies.
I've looked for people with the same problem as me, but I only found two people who had this kind of problem and they never got any good answers.
Does anybody know why this is happening? Is this the way this monitor "work" or should I try to make use of my warranty?
I hope somebody here can help me out.

Thanks!