Internal hard drive is not correctly recognized
I thought the hard drive in my MacBook Pro 13" 2010 was failing, because sometimes it would refuse to boot. I bought a new hard drive from iFixit. To my disappointment, it doesn't work either. I was not able to format it after installing it. I put the new drive in the external enclosure and connected it via USB. I was able to format it that way. Then I tried the same thing with the old hard drive. It turns out I can access either drive completely fine when it is connected by USB, but neither drive works when installed internally in the laptop. Disk Utility can see the drive but cannot format it. The error message is "Couldn't unmount disk."
Is it a bad ATA controller or something? Can it be fixed?
Is this a good question?