Is there a repair I can do to the hard drive bus on a MacBook Pro 2007?
I've changed the SATA cable but it still won't see the drive, which I know is good as it boots externally! Disk Utility doesn't detect it either.
If you're certain the drive is known to be good and working and that the cable you're using is also in good condition then the answer is no: there isn't anything you can do to fix a broken controller yourself. You'll need to take it to an authorized Apple Repair Center. These things are usually solved with main board swaps as it's all, more or less, integrated on one board in this case.