Bubkes, a few questions. I assume you have used CarbonCopy Cloner. If so, under preferences, have you checked the Make Bootable option under Target Disk Options? If yes, then open Disk Utility (Utility Folder within Applications folder). Can you see the partition? if yes, select and repair it. Then if you have Diskwarrior, use it to rebuild its file structure and try starting up from it. If this does not work, repair permissions on your original HD and clone again, in CCC check Delete directories... which is above the Bootable check. I would recommend that using DU you erase the partition before cloning, gets rid of possible crud. I do this all the time and my external HDs with 2 partitions each boot just fine. If this does not work, post back!