Mr PC wrote:
Are you set to use back button focus? if so, the camera probably won't fire until you focus it using the back button, usually marked AE-L, AF-L. It is on my D5200. The reset that Nikonian72 suggests is probably the quickest, easiest way back to default settings that will work.
The D3000 has no back button focus. The problem sounds like the camera is not focusing. What are the exact conditions when this happens? When the pre light comes on the camera is trying to focus so it is not getting enough light to allow shutter actuation.