My 400D has gone wrong - it was working fine this morning, this evening the flash has started firing spontaneously as I press to focus, while not firing properly when I take a picture. When I manage to take a picture the lighting is way too dim, and the flash then starts to fire spontaneously and repeatedly. I've tried resetting by removing both batteries, cleaning the lens contacts, and so forth. I don't even know if the problem is being caused by the camera body, the lens, or something else. I really need it, since I take most of my sales pictures with it, and if I can't figure out the problem in the next day or two I will have to buy another and worry about sorting out this one later. Since most of the test photos are taken with the M setting and no flash I can probably get by after a fashion, by using another camera for the product shots, but it makes things more complicated and I really don't need the hassle. Any suggestions?