Hi there. My name is Roger, and it would be my pleasure to help with your issue.
This error message is a general catch all for the camera. It can be caused by anything from a bad memory card to a sticking shutter. There's a few steps that you can try to get it cleared, but to be totally honest, this usually requires a trip to the shop to be repaired. Here's the steps to try.
First, power off the camera and remove the battery, memory card, lens, and any other accessories that may be removable and let it sit for a few minutes. Then try installing new or verified fully charged batteries only and powering it on with no memory card or lens installed.
Try pressing the shutter again and see if you can see the mirror flipping up. Also, here's a good step by step troubleshooting guide with pictures that will give you a good indication of what I'm talking about. CLICK HERE
I do want to point out that this is a common thing to occur with Nikon cameras when the batteries are dead or the battery has a bad cell and isn't properly holding a charge, so that also could be the case.
Hope this helps. Let me know if you have any further questions or if there's anything else that I can do to assist you. Please don't forget to click accept and leave a positive rating for me. Thanks and have a wonderful day!!!