Why does my computer screen bounce up and down sometimes?

Why won't new laptop screen come back on if computer is restarted or shutdown?

• My laptop screen got cracked and only half of it worked. I got a new screen for the same model and replaced it. I turned on the computer and not even the back-light came on. I then put the cracked screen back on, started it back up, and the screen came on. I changed the screen while the computer was still running and the new screen worked (and is currently working as I type this), but if I restart or shut down then the same thing happened as the first time. I don't know if it means anything but when the laptop is started up the Num Lock light is on and I can hit the key and the light will go off, meaning the feature is turned off, but I can only do this with the old cracked screen. If I try to hit the key after a restart with the new screen the light stays on. Anyone know why the new screen will not work after a restart but will if hot-swapped? Please please please help!

• Answer:

  Check for help in stores.