I have changed the hard drive in a 17" MBP, replacing the OEM with a Seagate 500GB, 7200. Cloning with SuperDuper was a breeze and the MBP booted from the new drive choosing Alt during start-up with no problems what so ever.

The problems occourd after the new drive was installed in the MBP. It shows the gray screen with the apple logo and the wheel is spinning, but it does not move on to the log-in screen.

I have switched the drive back to the external cabinet and it its still working fine from there, but for some reason it will not boot properly when mounted in the MBP.

I have done this before with another MBP with no difficulties, but that was before Snow Leopard.

Any ideas anyone?