Civilization 3 Demo

okay i'm wodering whether i should get Civ 3. I hear its good. So i went and downloaded the 380 Mb Demo and whenever i try to open it...

Kapow my monitor goes all funky.

the little green light turn yellow and it goes dark.
I turn it off and then turn it back on and for a moment i see an image of the screen. I can guide my mouse to the exit thing but i can't fix it.

i turn it on and off a lot of times and i finally exit and puff it pops back.

how do i fic this problem???