Help please

I have a question that I was hoping someone could help me with.
I am using Photoshop CS3 by the way.

My problem is that sometimes when I open my photoshop I can't use any of the tools such as brushes, the eraser, pen tool etc.
Instead of showing for example a brush that I want I can only see a small hand (hand tool) and even if I click on my picture the brush wont show up. I can't do anything. I have tried restarting the program and my computer but it doesn't work, it still only shows me that hand tool. Anyone have any idea why that is and how I can fix it?