Having trouble? Here are some of the codes that might come up on your Nikon D40x and what you can do:
Shutter release disabled: Aperture not set to highest f/number, memory card is full, flash charging, focus not acquired, S-exposure mode used after ‘bulb’ selected in M-exposure mode.
Camera does not acquire focus: Switch to manual focus.
Pictures are blurred: Shutter speed too slow. Use faster speed and/or tripod.