I'd suspect some kind of internal camera failure.
But before sending it off to Canon for repair, take a flashlight and check the pins in the card slot. It's quite possible that one or more of them got bent. If that's the problem, try straightening them with the end of an knife, if possible. Or, send it to Canon for straightening.
If not the pins, perhaps your card(s) need to be reformatted. First, reformat one card in your computer. Then put it into the camera and if the camera will allow it (ie, recognize the card is present), reformat it in the camera. If that doesn's solve the problem, it's off to Canon time...
