Hi, I tried to install a copy of Windows 7 by using rEFIt and NT6.x Fast installer on an external USB hard disk. After NT6.x Fast installer finished copying and modification files on USB hard disk's NTFS partition, I try to boot it from my iMac (2010 -27" i7 Core) but it showed following and stopped: "no bootable device insert boot disk and press any key" I plugged the same USB hard disk to my macbook Pro (2090 - 17"), it found and booted from NTFS partition and continue the installation. After installation, I could also boot Windows 7 from USB hard disk from my Macbook Pro. If I plug this Windows 7 installed USB hard disk to my iMac, it can't find the Windows 7 partition again. (It works again if plug to Macbook Pro.) I am completely loss because I don't expect this difference. I wonder if someone can help to finger out what is wrong.