Without a doubt, the number one reason a bootable disc won't boot is because BIOS isn't configured to check the CD/DVD/BD drive first.
O doro anya na ọnụọgụgụ nke a na-eme ka diski nwere ike ghara ibute bu n'ihi na a dịghị ahazi BIOS iji lelee CD / DVD / BD mbụ.