NEED HELP ASAP: "extend desktop" ability is gone

I have a Dell Inspiron E1705 (pos, yeah i know). I had the NVIDIA GeForce G0 7900GS in it, but the card died, so Dell replaced it with the ATI Mobility Radeon X1400 card. When this card was uninstalled, I all-of-a-sudden lacked the ability to "extend" my desktop onto a new screen. I can clone, but that's dumb and not what I need. So once it was in stock, Dell sent out a technician with a new 7900GS to install in my laptop, and I am STILL unable to extend my desktop. I've tried up-to-date forceware and all. Ever since this damned ATI card was in my laptop, it hasn't worked. What must I do to get it back? Would system restoring wayyy back to to when I had the old NVIDIA card do it?