From what I've seen with my macbook air, you can't boot an USB that just had installESD.dmg restored to it. You need some files from BaseSystem.dmg. The solution: This terminal app, it will make a bootable USB from the install mac os x lion.app. Usage: 1. In Disk Utility, format the USB as Mac OS X Extended (Journaled) and give it some name: We'll use USB Boot here but it can be anything. Make sure that "GUID Partition Table" is selected under "Options..." 2. Code: sudo install/mkboot Install\ Mac\ OS\ X\ Lion.app /Volumes/USB\ Boot/ Credits go to tseug from insanelymac, i just edited it to remove the hackintosh parts.