I have a dell inspiron 5748 that just did this. I reseated the drive, ran all the diagnostics, and the drive was clean. We then put the drive into a reader to see if it was dead. Nope worked just fine. It was the motherboard. I took the laptop apart(out of warranty) to see if there might be a loose cable and there was not a cable. the drive plugged directly into the board. So my suggestion is to remove the drive and have it tested. You can by a reader/repeater on Amazon for 20 bucks or see if a friend has one. If the drive is good then you know it's the board. I purchased an internal to external case for mine so it's now a back up external drive. I then parted the good parts of the laptop out and bought a new one.