Ah. I had the same exact problem. But then I read the manual. Crazy thing, that manual.
My guess is you're pressing the button you need.
The trick is, you have to hold it.
You'll then see a bar start to fill up.
Keep a good view until it takes the pictures (when both the crosshair things are green. You know what I mean.)
Hope I helped. I forget if it's the primary fire button or the secondary fire button, though.