Okay, I have a Maxxum 5D and I was changing out the memory in it. When doing so, somehow a pin was bent inside the card slot and at the same time, the camera would no longer turn on. I had used it just a few hours prior so I know it was fine earlier in the day. I thought perhaps the battery had just suddenly gone dead so I recharged the battery but it still won't come on. I'm really at a loss as to what to do at this point...any ideas what might be wrong with it, that would cause it to not come on?
If you can see inside the slot where the card fits, you may be able to see which pin(s) are bent. If you turn off the camera, and can get extra light (flashlight) on the pins, you should be able to see them. Take a fine-pointed forceps--tweezers--and straighten out the bent pins. When you think you have them pretty well straightened out, re- insert the card. If you have the pins close to the right orientation, the card will fit the pins. It has worked for me a couple of times!