Hi, I have Snow Leopard installed on all my machines: Macbook 2006, iMac 2009 and Macbook Pro 2010. I made a bootable Snow Leopard Install USB key. On each machine, when I press Option upon startup, and choose the USB key as boot drive, the following happens: -Macbook 2006: it all works; the green light on my USB key keeps flashing. -iMac 2009: 2 seconds after I chose the USB as boot drive, the green light stops flashing and nothing happens afterwards. It seems the USB key decides to stop working. -Macbook Pro 2010: same as iMac. Why would that happen? Is there any fix for that? Thanks in advance.