Gateway 19″ lcd tft monitor works on laptop – not desktop

I was given a 19″ lcd desktop monitor that supposedly does not work. Hooked to my desktop and it displys boot screen then goes black.
(Win XP Pro sv2, Nvidia GeForce6100 onboard video).
Hooked it to a dell laptop with an ATI Mobility
Radeon X1300 video adapter and the monitor works fine. Laptop running WinXP media. Does anyone have any clues?
Thanks..