Why will my Nikon D3100 not take a photo if the flash is on?

It works fine until the flash comes on via auto or I put it on manually. It just doesn't take the photo.

Added (1). Its nothing to do with the focus even when its in manual it won't shoot.

Check the settings. Look at the flash settings in the owners manual.

You have to make sure that the lens is focused… With auto focus on, ( side of your lens ) the camera will not shoot until the picture is focused