Remove the card from the camera and ( use your older card for this if you have purchased a new one) clean the card metal contacts with alcohol and leave them lightly wet, then work the card in and out of the slot multiple times. Next use canned compressed air to blow out the slot since sometimes the plastic spacers can break off of the cards and block the connection. It is also quite possible that the original card is defective (technology of this type does fail occasionally), and while one bad one would is likely, multiple card failures are not, in addition, reset the camera to the default settings, since a bad card can cause the camera operating system to misread. Also, if at any point you have filled the card close to it's space limit corruption can occur and cause this.
Please let me know the result. There are a couple more things to check
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You probably haven't FORMATTED your SD card in your camera using the camera's MENU settings, and that's why it's not recognizing your SD cards. This is where you should find it in your menu - Take a look at the pictures I sent.
If the camera is displaying "card error" with no card in the slot, the problem is most likely a contact component, in the slot, and the camera will not recognize the card to allow it to be formatted.