Virtually always when the shutter fails to release it's due to the thing under the AF sensor not being in focus. A quick test for this is to set the camera in manual focus mode - and I bet that the shutter ALWAYS fires. That's because the camera is trying to prevent out of focus shots in AF mode, but in MF mode it assumes you know what you're doing.
So what you need to do is to either ensure that things are in focus, or alternatively you can go into the menus and set the focus priority to release. (By default it's set to focus.)
_____ Brian... a bicoastal Nikonian and Team Member
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