Nikon D5100 won't format memory card?

My camera has been giving me error messages and not reading a single card for months now. I've recently learned it needs a firmware update. I have the update downloaded, and the card will read in my computer and I can transfer the firmware update but every card I have comes up with "card is not formatted, format card" when put in to my camera. I have gone to the menu, formatted the card, it will say format is complete, and as soon as I exit out of that menu it says "card is not formatted, format card" again. I've tried to format it with my Mac's disk utility and that didn't work, either. I have no idea what to do, I need my camera to work again but none of the instructions anyone has given me is working, and I know it needs the firmware update. Should I just send it to Nikon to be repaired or is there ANYTHING else I can do?