Reboot your system, and keep tapping (it is usually) 'Del' or 'F2' on your keyboard. This will open up the BIOS configuration Window. From here, you will need to navigate to the "Boot Order" (usually in the 'Advanced Configuration' option) and make sure your 'CD-ROM/DVD-ROM' is listed as the first option to boot from. Then your Hard-Drive (I, personally have it set to boot from Floppy Disc, then CD then Windows)
Sorry to come back with this thread again. After reading VOG contribution, which says at the end, that 'Once you finish booting from your CD/DVD drive, make sure that you change it back so that the Hard Drive Disk is first'. I am not sure whether it is harmful to change it and leave it to boot from the CD/DVD Drive. What do you think please ?