What is the best way to troubleshoot issues with a Nikon D40 camera not recognizing an SD card?

To troubleshoot issues with a Nikon D40 camera not recognizing an SD card, try the following steps:

1. Ensure the SD card is properly inserted into the camera.
2. Check if the SD card is compatible with the camera.
3. Clean the SD card and camera's memory card slot.
4. Try using a different SD card to see if the issue is with the card itself.
5. Update the camera's firmware.
6. If the problem persists, contact Nikon customer support for further assistance.