What error code are you getting? Is it (-E-) or CArd Err? If it's (-E-) make sure the cards are formatted in camera. It could be an issue with the memory card slots or damaged/faulty cards. I had a problem years ago with a D7000 that couldn't read new cards. Sometimes it recognised them, sometimes not. I got it fixed under the shop warranty (
LCE couldn't have been more helpful).
That's the problem with the internet, it makes there seem more problems than there actually are. I think it's because you hear about them whereas there would have always been a few problem cameras/electrical goods. There will always be a few cameras out the thousands they sell that will have problems. If there is an error rate of 0.1% (1 in 1,000) or 0.01% (1 in 10,000) that's not a huge error but they are selling thousands of cameras. With the internet you hear about that one in a thousand or ten thousand faulty camera.