Paint brush will not work with Adobe CS4?

Alright I am a noob when it comes adobe photo shop and when I was cooking dinner when my 17 month old Daughter was messing with my computer and some how I can no longer use my paint brush drawing tool. It is probably something simple but I need to finish a drawing ( I am making the design for a t-shirt for mt paramedic school class)
It is not locked
it does not work on any other image
I have shut down the computer
I am so confused please help!

I just got Photoshop CS4, and I was wondering why the brush minimum diameter toggle doesn’t work for me? Help?

Thanks a lot!
Edit: I mean in the brush window (or by hitting F5), there is a shape dynamics section. Under the size jitter option, there is a minimum diameter toggle. However, when I change it from 1% to 100%, it does not change. I have tried reinstalling Photoshop, but it did not work. Thanks!