I bought a SSD for my Macbook pro mid 2012 (Crucial MX500 500 GB, SATA) not even a week ago. It was functioning perfectly until today, when I saw a question mark folder icon on the screen of my laptop when trying to turn it on. I followed the Apple instructions to start the Disc Utility but the system doesn’t recognize the SSD anymore.
How can I solve the problem? Did the SSD just die? When I installed it in the first place I took care of followint all the steps to make it run properly and until now that just stopped ‘existing’ I had no problems at all.
If you have the 13" model, then replace the hard drive cable. This cable was known to have a high rate a failure on the 13" model. If this is the 15" model, then you could disconnect the power supply & battery and try reseating the hard drive cable on the Logic Board in case it came loose during the upgrade. If you want to confirm the internal hard drive cable is the issue (for either model), you can remove the SSD and connect it externally using a USB to SATA Adapter.
What version of OSX are you running? If it is OSX 10.13+, is the drive formatted using APFS or HFS+?
Did you perform a clean install or did you clone the system? If you cloned it, what utility did you use?