Blurry screen and can't fix it

i have recently installed xp service pack 2 and now my screen has become quite blurry, it is readalble but it is getting worse, this has only started to happen when i installed windows xp service pack 2. is there a way to fix this or do i have to use a restore point to get back to when i only had service pack one?

i have a dimension 4600 bought in early june btw,