Not having a 20D, I can't be sure what your issue is but we might be able to narrow this down.
The issue may be the lens and not the camera.
Current Canon EOS bodies have three focus modes... these are "One Shot", "AI Focus", and "AI Servo". If the camera is in "One Shot" focus mode, then the camera will _not_ take a photo unless it can lock focus on at least one focus point... but this is only true if the lens is in the auto-focus mode (AF/MF switch is set to AF).
This is because "One Shot" mode also implies something called "focus priority". That means the camera will NOT take a photo unless it can focus first. If it can't confirm focus, it will refuse to take a picture.
Try two things:
1) Switch the lens to MF and try again. If the camera takes the photo this time then it means the reason it wasn't taking a photo before was because it was not able to lock focus. If the lens is in manual focus mode then the camera will not insist on having a focus lock -- it presumes you deliberately intended to focus as you have and takes the shot anyway. Clearly you don't want to leave your camera in MF mode but we're just testing the focus priority feature.
2) You can also set the lens to AF, but change the camera to "AI Servo" mode. See if the camera will take a photo now. (never mind if it can focus -- we're trying to separate the "will the camera focus" question from the "will the camera activate the shutter and take an image even if it's a blurry image" question.) If it does take a photo then it helps confirm the focus problem.
Here's why: "AI Servo" is intended for sports/action. But AI Servo mode implies something called "release priority" (whereas "One Shot" implies "focus priority"). I mentioned that "focus priority" will not take a shot unless the camera can lock focus. But in "release priority" the camera will take the shot the _moment_ you fully press the shutter button and it will do this whether the camera was able to lock focus or not (so sports/action photographers know to half-press to lock focus before fully pressing the shutter and/or use back-button focus.)
If you can get the camera to take a photo use method 1 or 2 then it means the camera's ability to take photos is fine... and the real problem is the camera's ability to FOCUS is having a problem.
Focus, however, is part lens and part camera -- they both have to cooperate. It's entirely possible that you're having a problem with the lens and the camera itself is fine.
If this turns out to be the case, do you have another lens that you can use to test whether the camera can focus and shoot?
Lastly... assuming you have more than one lens but the camera has the same problem with all of them, then it would point to the camera. It's probably not worthwhile to attempt to service the camera, but don't discard the camera just yet. Canon offers a loyalty program which allows owners of Canon products to upgrade to new or refurbished Canon products at a fairly good discount. The defails of the program are not published online -- you'd have to phone Canon support, mention your problem with the 20D and ask about the loyalty upgrade program. Canon service can then tell you what products are available in the upgrade program (not all products are available.) They key is that you're basically trading up an old Canon product for a new or refurbished one -- so you don't want discard your current product even if you think it cannot be fixed -- until you can decide if you'd like to take advantage of the program.
Good luck and please let us know if you're able to get the camera to take a photo (even if it's blurry) using any of these methods.
Regards,
Tim
Tim Campbell
5D III, 5D IV, 60Da
