Formatted & installed OS has disappeared from new replacement drive!
I am trying to upgrade the hard drive in a a mid-2012 MacBook pro to a 1 TB Toshiba replacement drive. I formatted the new drive, downloaded a clean version of OSX from Recovery (I think Mavericks, at least that was the background image), and set up the system. All of this I did with the new Toshiba drive attached as an external drive to another Macbook Pro. I was able to give the new drive a name, and all seemed well.
The new drive mounted fine as when mounted from the other laptop, I could see all the standard OS installed files on it.
When I installed the drive into its new home in the old Macbook, it's not recognized in any way (continuous flashing question mark). I went through the process of mounting it as an external drive attached to the other Macbook, and tried to set the new OS as the startup (and thought it worked), but it still wasn't recognized when put back into the laptop. It's not the cable; the old 250 GB I want to replace still boots fine.
Then I tried to do a complete new Recovery format and install (while the drive was in the laptop), but Recovery couldn't find the drive either.
Now when I try to go and retrace the original steps (formatting the new Toshiba drive from another MacBook with Disk Utility) the new drive won't mount anymore. It's totally invisible/uncommunicative.
I think I understand that there's a difference between an external bootable drive and an internal bootable drive, but right now I can't get to the drive at all, to do anything with it or make changes.
What happened, and how can I fix it??
Is this a good question?