20D error CF

I got a new 7D recently and sold my old 20D to a close friend.He is now having problems with the camera and I am trying to help him.When he turns the camera on nothing happens until he pushes the shutter button, then it displays "error cf".I bought this camera new about 5 years ago and it has never malfunctioned.I gave him my old cf cards and everything worked fine until recently.I'd appreciate any help as my friend knows nothing about cameras and maybe with your help we can get this camera back up and running.Thanks.

Does this happen with just one card, or has he tried several of the cards? Looked inside the card slot to see if he's managed (it isn't easy to do) to bend a pin? Backup battery still good?

Hey, I got to look at my old camera and it is a bent pin.He bent it over so flat that I was unable to catch it with anything.He will take it to a camera repair place to see how much they want to fix it.Thanks