Nick,

As indicated by John it is worth cleaning the contacts of both camera and lens.

You have not indicated what lens you are using and if it has a focus distance limiter switch. If you are not within the focus range you may not get a response from the shutter button.

You have not stated if you are getting an error message which you normally get when there is a contact fault. If you are not getting an 'error message' then this may be a good sign.

If you are not focused within the distance limiter range I can see it as a strong possibility that the camera may not respond. That being the case, set the lens to manual focus and refocus within the distance range. Once you have done that put the lens back to 'focus on' and use as normal.

All of the above does not mean you are out of the woods yet. You need to go to the camera menu. Go to the 2nd icon from the left which is C.FnIII and depress the camera 'set' button to open up that function. Then go to '1' which will indicate options for 'Focus search on' or 'Focus Search off'. When you have 'Focus search off' it acts a bit like the distance limiter on your lens. You have the option to put focus search on which will enable the camera to hunt throughout the focal range (this will slow down focusing since the there is more distance to hunt). FYI I have 'Focus search off' 95% of the time and pump the focus from where the lens is focusing to where I want it to focus by keeping lens focused on the ground moving the lens to where I want to be at. This sounds complicated but I do pre focus without using the switches instinctively and enables me to gain very rapid focus.

in addition to the above if you are in an unsuitable programme mode (or focus option) which offers multiple focus points your camera may have difficulty locking on and will not respond when you press the shutter button.

Finally even when everything is working OK you will not get a response when pressing the shutter button because the camera is confused by the scene it is shooting or that there is not sufficient information or detail to get a lock on e.g. when the light is bad and there is little contrast between bird and background, when that bird is too high in the sky and it barely covers the focus square in the view finder, when you are shooting across air turbulence or air that shimmers or when focusing in a busy area where there are lots of small twigs (especially in a breeze) all theses things and others can prevent locking on.

Good luck.

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