It will void the warrantee if you make it obvious, like pry marks trying to open it, striped screws.
What kind of monitor is it? (Make and Model) You take the chance on voiding the warrantee
when you try and fix it yourself, but sometimes it pays off. Its going to cost anywhere from
25.00-60.00 to ship it to the manufacturer and then you might be in for a wait.
A couple more questions, does adjusting the refresh rate make a diffrence on the focus?
Also have yo tried it on another video card just to make sure its the monitor.
You dont have any speakers around it either right?