Try running Disk Warrior on it, and a repair permission (And Repair Drive from Disk Utility)
If that doesnt work, may just need to wipe the drive and reinstall OS on it. Perhaps its a corrupt install.
Good point!
Intel Mac's will not boot from non GUID formatted drives. But they will show up on the desktop once the intel Mac boots normally from a GUID formatted drive.
Some older USB Bus Powered drives require a Y adapter. One end (USB Mini) plugs into the drive, the other end Y has two USB plugs for the computer, one to power the drive, and one to transfer the data. See...
I have a 1TB drive from OWC that is both Firewire and USB (Bus Powered)
http://eshop.macsales.com/shop/firewire/on-the-go
It is partitioned into 5 partitions
10.5 Diag - 30GB
10.6 Diag - 65GB
10.5 Installer - 13GB
10.6 Installer - 13GB
and Extra - that holds files. - 810GB
On the...