Fill isn't working...

I am trying to make a front cover for a Uni guide I'm doing, but edit>fill does nothing.

I am following a tutorial, which says create a layer, edit>fill>50% grey

I did that, but nothing happened...

Any ideas why?

it happens, just restart the photoshop!

Might have the wrong layer selected

Try it with the Paint Bucket Tool?
Make sure the layer is visible and selected.

Photoshop CS3's other functions don't work properly I guess. Sometimes even the close button doesn't work.

i use cs 3 and it works fine for me!