I have ATI on my Windows 7 computer but it is different to that.
What I don't understand is you say it works alright upstairs but not downstairs
All I can think of is something to do with the upstairs extended monitor must be different to the downstairs one, is one and old style TV or a computer monitor and the other a flat panel LCD with high definition or plasma ?
Are you connecting them both with the same type of connection lead ?
What sort of connection are you using ? (HDMI, Video RCA, S-Video or Converter box of some type).
It may be to do with the resolution setting on monitor 2.
when your in the dialog where you see the 2 screens side by side select the second monitor and try changing the resolution for that monitor, it should show the resolution with a drop down box for selecting alternatives, also make sure it is set to extend these displays.
Then when you select monitor 1 check the resolution showing for that and if it shows a black border on your laptop try altering the resolution.
I'm off to bed now so can't answer any more till tomorrow.