I experienced an odd problem with my 40D. Whilst trying to use exposure compensation using the Quick Control Dial, I found that it would not work. The on off switch was in the correct position. I then tried setting the camera to manual and could not alter the aperture - it would not budge from the smallest aperture for any lens that I tried. Switching on and off, and removing the battery had no effect. Finally I reset the camera to factory setting and this solved both problems. Question, does anyone know of an explanation or is it one of those unexplained things that happens with things that rely on computers?
Remember...a camera is a special purpose computer with all the problems inherent in this world of electronics. Just as your PC will hang-up and you re-boot to get it back to normal again, you needed to do a similar thing with your camera.
I have to say that i was not really worried about it being a harware faullt. You only have to think about the Blue Screen of Death with PCs. As you say the cameras are computers with optics built around them.
Thinking of odd things. I have an Canon ST-E2 transmitter that I was experimenting with once with a 5DMk2. I was wanting to use the transmitter's infrared beam to focus the 5DMk2 in a darkened room that was outside of the ability of the cameras autofocus capability. No flash. I could not get it to do it. I happened to be going to B&H and thought I would pose the question to the Canon guys that I've heard were quite knowledgible and they told me it wouldn't do that . I was sure it would because I could get it to do so with my 40d (later sold). I called Canon customer service who said it should but all settings they tried including restore defaults produced no change.They lined me up to send it in and then I noticed the camera was not on single shot mode as I had used with the 40D. That was the problem but nothing in any of the manuals mentioned a thing about this type of usage for the transmitter.