Try a hard reset:
Remove the battery, memory card (if installed) and disconnect any usb cables. Switch the camera on . Allow the camera to sit idle for 30 minutes. Switch the camera off. Reinstall the battery without the memory card and try to power on. If there is no response, plug in the USB cable and connect the camera to the computer and note any activity.
Please let me know the result.
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When you power the camera on with the memory card removed, do you still get the error message or does it only display once the card is installed?
What are the sizes (capacity in mb or gb) and the type (CF, SD or SDHC) that you are trying to use?
Good morning! Do you notice any unusual "whirring" noises? Does the lens move? Please let me know. The system error message on a Nikon can mean almost anything, It is a very general message letting you know that something is wrong. I've had it before, and the problem was that I had taken it to the beach and there were a couple of grains of sand obstructing the lens motor gears. I won't be taking it back to the beach! The casing has a multitude of openings that welcome unwanted particles.