This was an odd one with a simple fix!   I recently had to upgrade a Dell Inspiron 1545 to an SSD drive, however after cloning the drive and installing it in the machine, the drive was just not detected?   I tried a BIOS update but that didn’t help?

The SSD drive I was using (crucial MX500) was a little thinner than the spinning drive I took out.   The Crucial drives come with a plastic insert that sticks to the outer case of the drive to make them thicker.   Once this was in place – everything worked perfectly!

Really odd, as it looked like the drive should fit into the connectors, but it must’ve been just missing them given the size difference!

Worth a try if you hit the same problem – hope this works for you and saves you some time!