By changing the BIOS boot order , you can force your computer to boot from a CD/DVD drive, a floppy drive, or USD Flash disk. Changing the boot order on a PC is mostly done in order to boot from a recovery disk (like Active@ Boot Disk) to run some kind of data recovery software, partitioning utility or password reset tools.
Read the original here:
Start computer from CD, DVD or USB Flash drive. BIOS setup settings to boot Windows LiveCD.