Unable to draw on layers

I just opened a new file and am unable to draw on any of the layers. Nothing is locked or hidden as far as I can see, but when I click on the brush tool and try to draw nothing happens. I have never had this problem with opening new files in the program before. Any ideas what I am doing wrong?

I am working in a free trial version, if that makes any difference.


Have you tried opening an old file and seeing whether you can draw on a layer?