camera wont take shot when shutter pressed

I seemed to be putting up a lot of silly post it might appear to some but im lost and confused when I went out this afternoon and in full sunshine and blue sky and moon was in the sky so dicided to take a photo set it to A on camera and focused and through the lens it appeared a clear shot but when I came to press the shutter to take photo nothing was happening I physically coudnt take a photo anyone know why ????. in the view finder iso a was flashing and I don't know what that means either....

Flashing ISO usually means auto ISO is on. Did the camera obtain focus? You need good contrast to get a focus lock. And if your camera did not lock focus then it won't fire. What were the camera settings?

it was on A with iso auto setting for day light but the focuscing was slightly blurred but when press once more quickly it appeared in perfect focus but couldn't do anything with the shutter release button.

Sounds to me like your camera could not achieve focus lock and the camera settings are such that you can't take a picture until you DO have a focus lock. Things may have looked in-focus to you, but our cameras sometimes have other ideas about this.

You can change a menu setting, however, so that you can take a shot even without your camera having a lock on focus.

....

Also the camera wont fire if you have no card inserted. Not being funny, but that happens to me a lot. Taking it in and out to view shots on the computer this happens a lot.

ISO can be set to "Auto" but if it is set to limit it to a certain ISO it may not have allowed the exposure you needed to get shutter release.