I have two twin MBPs. One failed to boot showing the flashing folder & question mark. I do have good Time Machine BKs for this system. I placed a new non-apple HD (1TB). I formatted it as a apple extend file jounaled file system. Used a bootable USB with Disk Utility and downloaded and installed a fresh copy Lion. Then connected the Time Machine backup and restored to a desired point. Before a restart all looked good. After a restart I still get the flashing folder/?. Even pressing Option at restart fails to show the new HD as an option. I removed the new HD, attached it to the system via USB connector, selected Option at power up and was able to see the new HD and the system booted fine from it. But the system fails to boot if the HD is attached internally. I suspect that I missed or goofed on the GUID partition. Or was that automatically created when I did the Lion install? If I missed the GUID step, how can I fix it at this point? Either using some tool to write the GUID to the HD or starting over and reformat the new HD. Thanks for advice in advance.