Use a CDRW, not a CDR. I was using an HP CDRW disc and was having problems, only would boot maybe once in 5-8 tries. Then I formatted the disc, full format not quick, and then reburned the ISO. Once I did this, it boot every single time for me using the same disc that was causing problems before. May not work for you, but just suggesting something that seemed to work well for me.