are you multi-booting? If you are maybe try to boot using different OSes and see if it has any effect on the screen. If so it would mean that there is a driver problem somewhere.

It has nothing to to with drivers Im afraid. Its dark all the time, even the bios-text at the beginning.

But why is the backlight broken on the regular monitor and the external one that you tested?

It sounds like the backlight gave out, but in that case why would a second monitor also show up dark?

My guess is that your graphics card is faulty, perhaps as result of a power surge. It's easy to burn out only one component of a computer with a power surge--it happened to me with a nearby lightning strike that took out my SBC-supplied DSL modem and also the Ethernet card it was attached to. Nothing else in the computer was damaged.

If it wasn't a laptop I'd suggest borrowing a graphics card from a friend to see if it would work. But that wouldn't be feasible in most laptops.

The flashing before the darkness occurred doesn't sound good to me, and is the main reason I think the graphics card is damaged.

Sounds possible. It is most likely the graphics-card. Perhaps I could open it and check if there is anything visible. If there ain't though, I guess there is nothing I can do. Perhaps leave it for repair somewhere...