Leonardo has the right idea. Try another monitor to see if it is the screen or the video card. I see no possible way your laptop could damage any external monitor you connect to it.
If the flickering reacts to moving the screen around or bumping it, then it may be a lose connection. If you are mechanically inclined, and the thing isn't under warranty anymore, you could take it apart far enough to find the connector for the screen and see if it is seated right. Laptops are kind of like onions when you take them apart, there is layer after layer of pieces you have to unscrew and remove to get to the next layer of pieces to unscrew and remove. Fortunately, the place where the screen connects is usually one of the top layers.
However, if you have doubts about your ability to take it apart or put it back together, I wouldn't mess with it. My old HP laptop (can't remember the model) had some horizontal lines that would flicker throughout the screen. When I opened or closed the screen this flickering would get worse, sometimes just tapping the back of the lid or jolting the thing would cause the flicker to start, which led me to believe it was a lose connection. Taking it apart, unfastening the ribbon that connected the screen to the motherboard, then reconnecting it fixed the problem for me.