40D refuses to fire

Hi, my 40D refuses to fire ONLY when I have a cf card inserted. Without a cf card it fires normally. Does anybody know what's wrong with it? I tried searching this problem but I couldn't find anything besides the shutter problems. Really sucks that my camera just started doing this before the holidays

Try a different CF card in case that one is bad and check for a bent CF pin.

You can also try and do a reset to factory default in the menu. I have found sometimes to that removing all the batteries and then pulling the small backup battery has solved the problem on other Canon camera's that have had the same problem.

Thanks, I have tried multiple brands of CF cards and all the pins are intact. I reset the camera back to factory default and the problem still persists.

You have probably tried, but I will suggest anyway just in case, have you reformatted the cards in camera? Are you getting AF confirmation? What mode are you shooting in, green box, manual, aperature priority? Man, that is a tough one, also, have you tried shooting tethered to a PC with the EOS utility? That would show if it is a camera problem, card problem or possibly a card write problem in camera. Hope some of this helps.... gotta suck...
David