Problem with external screen.

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http://www.linuxquestions.org – I just downloaded linux and instaled it. Ok so far, i rebooted and selected Ubuntu, a loading screen comes with ubuntu and a purple background, but the screen trembles a little. After the the loading ends my external screen blacks out and says No signal found 3.2khz 4.7hz. Also, i use laptop and my screen is broken, when the message (no signal found) to my external screen appears, my laptop's screen opens. The problem is, my laptops screen is so badly broken i can't see a thing. Is there a problem with my external screen, like it needs drivers or is there an option to ubuntu about external scr (HowTos)