Answer to: SSD will not show up after installingMake sure the new drive is initialized. Sometimes they aren't and until it is nothing will see the drive. Not much of an Apple guy but I know from lot's of experience with Western Digital I would have to hook the drive up to a windows machine with Hard Drive USB reader and use the Disc Management app to initialize the partition on the drive. May be the case you are facing here. Once done I then had no issue installing to the drive etc. I know you mention that the OS was able to see the drive at one point. I would just make sure that the drive is showing up correctly and that the partition is fully initialized. Can be done with a $25 hard drive reader and any computer system. Plus it is just a handy thing to have.