If you turn it on and set the screen to black (set the destop background to black or something like that) do you see the scratch light up white?

If so, you've managed to go through the polariser to the screen. There isn't much you can do in any case, as the polariser and matte finish layer are bonded to the front of the panel. It's possible to remove them by correctly applying a solvent (usually water!) and waiting, but I doubt there's any real way of replacing it. If it's an expensive monitor it might be worth getting a new panel for it, if not it's an insurance job I'm afraid.

Pca