Wonder if anyone can help. I have a new MacBook Pro running OS X 10.6.4 I wish to create a bootable backup of my Macintosh HD on a LaCie 500GB USB external HDD which is 2-3 years old. I formatted the drive with a GUID partition table scheme, with the volume formatted as Mac OS Extended (Journaled), which I believe is the correct setup. I then used SuperDuper! to backup all files to the external HDD - no problems there. However, when I try to boot from the external HDD by holding down Option key during startup, I do not get the boot menu, instead the computer freezes at a blank grey screen and doesn't boot anything. If I remove the USB drive and do the same, the boot menu appears with Macintosh HD as the only choice (as would be expected). I have tried holding down Cmd+Option+Shift+Del during startup - this doesn't work either. Can anyone shed any light on this? Is it a problem with the MBP or the external HDD? Any help much appreciated.