Graphic prob!

I have a core I5 notebook with 6 gig mem and 1 gig dedicated graphic card.. card is Radeon 6490.. Here lies the prob, I can hook up to a 19" monitor to play anno 2070 on full spec for example and no probs.. If I play nolimits on the notebook with full spec again no probs but with the monitor plugged in the game goes laggy and stutters!!! Do I need to update the opengl drivers? if so how? and while I'm at it in the game setup section what is dithering and do I need it on? cant see any difference on or off and the fps fluctuates between 60 and 70+ with fps limit off.. some help with the above would be greatly appreciated.

I'll try to help if you can write your post in coherent English. As it is, I can't even tell what you're asking.

What's the refresh rate for the monitor set at? You may need to change it.

[Goku1910]

is your laptop monitor off while the external monitor is being used? I know some OpenGL apps don't play friendly with dual monitors.