Got Win 7 iso file and transferred it to a usb following procedures by boot camp assistant. After creating a boot camp partition, computer reboot and I can select language under Windows. But after I click install, a black screen appear saying "no bootable device -- insert boot disk and press any key". I am now stucked here and cannot go back to OSX even unplug and reboot. How can I go back to OSX? My USB should already be a bootable disk. Why the computer still say no bootable device? Thanks for any advice!