Photoshop wont let me use the brush tool.

A few days ago I was working in photoshop when all of a sudden my brush tool stopped working. What happened instead, was each time I selected the brush tool it would automatically change to the eyedropper tool as soon as I tried drawing something. I've tried resetting my brush preferences, I tried reseting photoshop and I changed all my presets to default. Nothing has worked and this is really getting annoying. Is anyone else experiencing this problem or have in the past? I have a deadline coming up and I need to resolve this now.