New to CS4 not sure why I cannot use my tools on an image...?

First time this happend I learned that I had to go to Mode and change the images from Index color to RGB. Now, however, they're rgb and saved as a psd file and I open one up to do further edits and instead of allowing me to grab a tool and use it I get the hand pointer. I'm sure its something simple but I can't figure it out. Please help!!!