I've successfully burned a Ubuntu boot DVD from OS X (Snow Leopard) on my Macbook Pro. The problem is, the built in optical drive kicked the bucket a few years ago and I've been using an external optical drive that connects via USB. When I try to boot Ubuntu from the DVD in this drive, it looks like my computer doesn't even recognize the drive during start up. I hold alt while the computer turns on and it only gives me the option to boot OS X from the hard drive. Any suggestions?
Don't worry ! You can install Ubuntu using another way, I think USB Bootable is good method, You can create Ubuntu Bootable USB Pen,plug you pen drive and open Startup Disk Creator, make your bootable pen drive