Tried 1.) Installing SL from USB -- Apple logo and nothing 2.) Installing SL from DVD -- Apple logo, disc spins, nothing 3.) Download DP2 update, launch dmg from desktop. Get error: "This disk cannot be used to startup your computer" --> hint? This worked for my Air, just running off the desktop. Possible issue, I installed Refit on this computer a long time ago (this is not my primary computer) and I think that it has messed with the EFI so that it cannot boot from things, how do you restore the stock EFI? should I delete something? I took the steps that the website gives to uninstall it. WTF!?!??!?!?!?!!??!?!?!?!!?!?