I've been using a 32gb card in my 90D for some time and it was fine until this week. Now the camera says No Card in Camera when I switch it on. I've tried another card and that is fine. However the card it doesn't appear to see is fine when I put it in my PC. Any thoughts on how to deal with this other than throwing away the card?
Canon uses the Fat32 or exFAT format depending on the card and camera. So if the formatting doesn't match up it could be problematic, doubtfuul that is the issue if you own a PC and use this card just for the camera. You could use just a dab of isopropyl alcohol on the end of a q-tip and see if you can clean the contacts on the card a little bit, in case the camera is just a little bit finicky compared to the computer. Card may be starting to die in any even, you may want to consider it unreliable going forward.
Cards sometimes go bad. I just dug out my Panasonic Lumix FZ50 yesterday and when I turned it on, it prompted me to format the card that was already in it. When I put the card on my computer via the USB card reader, it was not recognized, so I put it back in the camera, attempted to format it and got a "Formatting error" message for my troubles, so I popped it out and tossed it in the trash. Fortunately, 32GB SDHC cards are pretty cheap these days. Just get another one and don't worry about it. That said, if you get multiple card read errors with the same camera, you might want to look into replacing it, which will definitely be a bit more spendy than a memory card.