Which specific 5D do you have (original, Mark II, III, IV)?
How old are the CF cards? What brand? Though since three are no longer working, that sounds like you're camera has an issue. Depending upon its age, you may need to see about doing a repair.
YOU accept a comment as a solution, or not, by clicking on "Accept as a solution". Maybe you did it accidentally.
All the same, if multiple CF cards are not being recognized by the camera, either they all went bad together (not likely), or there's a malfunction with the camera. If all the pins in the camera are intact, what's left is the camera needs to be seen by a repair service.
Have you used a flashlight and a magnifying glass to carefully examine the pins in the CF socket in your camera for either bent pins or dust and dirt in the socket? With 3 cards not working, it seems that there is a problem with the socket or electronics in the camera. If they appear to be ok, then the camera needs servicing or replacement.
09/26/2023: New firmware updates are available.
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