Changing the monitor should make no difference - did you change somthing else at the same time?
The "vertical lines when scrolling" symptom is to do with the display (graphics card) drivers. Usually they vanish when the system catches up with your actions.
You could try updating your graphics card drivers. If you need help with this please ask. If you're not sure what graphics system you have, you can download Everst Home Edition free from here click here which will tell you - and also many other details of what's in your system.