Alright heres the situation, I recently got a Macbook Pro (Late 2007) from a friend for free, and I wanted install Lion on it to use it. The Super drive doesn't work , and the internal HDD sata cable is broken, so I have to boot off an external USB HDD. I made a bootable USB with Lion on it, and while it worked with my Macbook Air, when i try to boot from the usb on my Pro, a gray circle with a line through it appears, and it cannot boot. I decided to just boot using my air and install Lion on my external using my Air, but after I installed, my Pro STILL couldnt boot from the HDD , it had the same error, the circle with the line through it. The HDD works fine, and I can boot normally from the external with my air , but not the pro. Any ideas, I am stuck and really want this to work 