I am trying to clean install Mountain Lion on a Mid-2009 MBP (http://www.everymac.com/systems/app...3-mid-2009-sd-firewire-800-unibody-specs.html) However when I attempt to boot from USB by holding down the Option button I only see the Macintosh HD and the Recovery partition for Lion. If I unplug and replug in the USB drive the computer freezes, as in I cannot select any drive to boot from using the trackpad or the keyboard. If I unplug again I get the little poof cloud, sorta like when removing a shortcut from the Dock. I have tried SMC (http://support.apple.com/kb/HT3964) and NVRAM/PRAM (http://support.apple.com/kb/HT1379) and rebuilding the USB key using Lion Diskmaker. With the same USB drive I updated my MBA to Mountain Lion early this afternoon. Any thoughts? Thanks.