screen flashing when I connect projector

Hi
I need some urgent help. I have a laptop Acer Aspire 5100-3949 with AMD
Turion 64 Mobile, ATI Radeon Xpress 1100, 1 GB DDR2 and Windows Vista Home
Premium
I have a multimedia projector SHARP model XR-20X/XR-20S
So when I connect the projector to the laptop, after 2 or 3 minutes, the
screen began to flashing until unplug the multimedia projector from the
laptop…
I have no idea what is the problem…. I tried to change the display
resolution (put 800x600), get off the theme aero of windows and put classic
…but nothing happens,…
First I turn off the laptop, then connect the projector, then turn on the
projector and turn on the computer, then every thing works fine for 4 or 5
minutes, and then the screen begins flashing, and falls in a loop with
windows trying to change the display resolution.
So I don’t know what exactly I have to do; I connect the laptop an CRT
display and it works fine, and I connect the multimedia projector to another
laptop and other pc and it works fine… only that this pc and laptop was
running windows xp not windows vista…..
So I was thinking to change the windows … to put the ultimate but I don’t
know if that is the solution….. what if I change to windows xp sp2?