MacBook Pro 13" Drive OK but system wouldn't boot

Mi Problema

The MacBook Pro would boot in disk target mode with the original hard drive in an external USB enclosure. However, it would not boot with the drive internally on the SATA cable.

Mi Solución

Swapped out the SATA cable assembly, put the new one in very easily (but carefully). Put the MBP back together and we were good to go!

Mi Consejo

Be very careful not to overtighten any of the SATA mounting cables. They are very shallow and very tiny!