Why isn't my Nikon D300 actually taking a picture?

Hi! So i recently got a Nikon D300.So this morning, i went to take a picture and it won't take it! It focuses and all, but it won't actually take the picture. My memory isn't full, I'm on P mode. I don't know what is wrong with it? The reason I'm asking is because I don't know what to look for in the manual. I'm new to photography and complex cameras. I got this from my fathers friend.

Look at the switch on the front of the body labeled S, C, and M. If it's on the "S," the shutter will not release unless the focus locks. There's a little green dot on the bottom left of the viewfinder that will turn on steady if focus is locked and it will blink if it's not. If it's blinking and the switch is on "S," the shutter will not release. Chances are you are too close to the subject to focus.

Your other choice is to use either C or M, because the shutter will release whether you have locked focus or not.

Did you take the lens cap off?