The mic on my netbook works sometimes as I move the screen forward, how can I repair it? thanks

Sounds like a loose wire! there is nothing you can do without opening up your laptop but if you aren't afraid to do that then you are in luck.
this is generally a good how to on opening up any laptop http://www.ehow.com/how_4826335_open-hp-pavilion-laptop.html
following this, find the wires directly under your mic and that should be where the problem is

You probably have a bad cable going from your motherboard to your screen. The hard part is figuring out which cable that might be. Could be a power cable, or audio cable. If your able to, take the laptop apart and see if any wires look messed up.