This (or something like this) happened to my dad's pc. I had donated my old ATI card and installed drivers, but after reboot there was something a little off and looking at it made me go nuts
It was slightly out of focus but in a weird way, and I know it was relatively easy to fix. I can't remember exactly but it was either at the wrong res after install or I used the monitors auto-adjust. Still, your problem could be entirely different so goodluck.