Hi there. I have a new MacBook Air running Lion. Every time I use my backup software, it changes the permissions on my external drives, and I have to change them from read only to read & write, so I've gotten into that habit.*At one point, I noticed that the permissions on my internal *startup disc* were read only, so I (foolishly, I now know) changed the permissions on the startup disc to read & write, with apply to all enclosed items checked. As I continued working, I got messages that a number of extensions could not be used and will be disabled (or something like that). I decided to reboot, so the computer could reset and hopefully correct things. When I tried to boot, it hung up on the grey screen with the Apple logo and the spinning clock/gear. I let it spin for a while, then forced power down and tried to boot in safe mode. The progress bar appeared as it's supposed to, but when the progress bar finished, it went back to the grey screen and hung up again. I let it spin for over 40 minutes before powering down, just in case it was doing diagnostics or something. I am traveling in Nepal, so I don't have access to the original OS DVD (nor do I have an optical drive to put it in). And I'm so very far from an Apple Store. Any suggestions for getting the computer to boot, at least in safe mode? Thanks for your help!