"This is actually a pretty common problem that has recently become more complex.
Your computer’s BIOS needs to be instructed to check for a bootable CD or DVD before it tries to load whatever is on the hard drive. Right now, your computer is configured to either ignore the CD/DVD at boot time or check the hard disk first.
Oh, you don’t have a BIOS? You have a newer machine running UEFI?
Well then things get more complex"
As more people move to Win8 and beyond this question will be asked more often.. ask Leo, I'm busy!
http://askleo.com/how_do_i_boot_from_cddvdusb_in_windows_8/?awt_l=JDlCF&awt_m=JbKGF14vhJdfbL
Your computer’s BIOS needs to be instructed to check for a bootable CD or DVD before it tries to load whatever is on the hard drive. Right now, your computer is configured to either ignore the CD/DVD at boot time or check the hard disk first.
Oh, you don’t have a BIOS? You have a newer machine running UEFI?
Well then things get more complex"
As more people move to Win8 and beyond this question will be asked more often.. ask Leo, I'm busy!
http://askleo.com/how_do_i_boot_from_cddvdusb_in_windows_8/?awt_l=JDlCF&awt_m=JbKGF14vhJdfbL