Illustrator starts beeping after creating a new layer?

Hi,

I've been trying to make a new layer underneath lineart to draw in, but every time I create the layer, Illustrator just beeps at any kind of input and I cant get it to stop without restarting Illustrator. Even then it just doers the same thing when I create a new layer. Has this happened to anyone else and do you know what the problem is and how to fix it? I have also checked and no new windows open when I create the layer.

Thanks!