This may be obvious but I have attempted to boot from a bootable USB on my MacBook Pro (2011, running Lion 10.7.5), the USB does boot but fails to finish the full boot process (it is a Ubuntu derived bootable linux USB).
In terms of what happens during boot, well it goes to the grub options and after selecting, it will start to boot, get to a certain point and then "stop" and hang with nothing on the screen.
I have used this same USB to boot into other, newer MacBooks with success.
Has anyone else run into this issue?
NOTE: The usb is formatted FAT32
Best Answer
MacBook Pro before 2012 don't really support USB boot (that's why when you install Bootcamp on these machine it requires the Windows CD). You needs to burn it into a CD, if you want to make changes to that Linux, you have to install the system into a partition of your 2011 Mac hard drive, then make change to that partition.