I have 2 Dell C840 notebooks that have the same problem.
Everything, including toolbars and taskbarsappear much smaller than they should.
The display covers the whole screen on 1600 x 1200 resolution.
Sites like yahoo that usually fill 90% + of the screen, now covers about 60% and looks like an old style website centered with large empty borders.
I will admit that one was working and looked normal, but having simply removed and replaced the Video card, it altered its looks to the same small view as the other.
I have downloaded a nvidia driver from microsoft which in Device Manager, Display adapters is called Dell C840.
It states that 'This device is working properly'.
Please let me know if you have any ideas.