Around last Thanksgiving, the internal flash on my Canon 40D camera started to act up. I couldn’t get it to pop up. At first I figured that I messed some configuration or something. I kinda ignored it for a few weeks; I tend to avoid using the flash as much as I can anyway.
So finally with some free time last week, I finally looked into the fixing the problem. When I digged into the configuration of the camera, it became clear that it incorrectly detected the attachment of an external flash! This explains why I couldn’t get the internal flash to pop up. Figured it had to be some mechanical issue like a pin getting stuck or something. I used one of those air canisters to blow some air on the horseshoe to clear out any dirt and sand. When that didn’t work, I used a tweezer poking around the horseshoe. Lifting the metal plate on right side revealed this tiny pin. Giving the pin a little wiggle via the tweezer did the trick. The pin popped up and the camera no longer detected an attachment of the external flash– the internal flash popped up just fine, finally…
Don’t know if this is common, but other 40D owners have definitely seen it. Found a useful thread on flickr with very insightful discussions.