This is a more or less common issue with the 40D (and as far as I know 30D and 50D as well, because same shutter button unit). The shutter button is most likely not working because of some kind of dirt in it. There are two possible solutions I know of. Both aim at the goal of cleaning the button with use of cleaning fluid suitable for electronics. 1st: Complicated but "safe", dissasmble and clean the button part by hand. - you should be able to follow this instruction to get to the button unit: Canon EOS 40D Shutter Button Replacement (The instruction is not from me) - clean the shutter -- a) either by disassembling it completely and clean every single part of it -- b) or by just soaking the button unit in cleaning fluid and pressing it several times - let it dry and take it back together 2nd: Quick'n'Dirty but maybe "unsafe", dont disassamble, just pour the cleaning fluid into the battery compartment - remove both batteries from the camera (the main battery as well as the little time-save-one - prepare a...