you need to set the boot order in the bios,
you want to set it to boot from the dvd drive and not the hardrive.
do this by pressing F12 on start up. at least its F12 on my machine.
however. there are people more qualified that i to instruct you how to clean install .
and the steps you need to take to make it more successful.
hang tight and you will get the help you need soon.