Samsung Series 9 15" Premium Ultrabook

guys i'l make this as short as possible.

I bought a laptop Samsung Series 9 15" Premium Ultrabook last week, now i have a windows 8 pro installed with this laptop. I try to format and change this to windows 7 but i cannot boot it on the CD rom or USB.

here is the exact model that i bought on this site:
http://www.samsung.com/us/business/laptops/NP900X4D-A04...



I already check on google and youtube to get some advise but still I can't let it boot on a usb or CD rom if anybody could help will be much appreciated? thanks in advance...

and by the way here are the sites that i followed and it didn't work:

http://www.youtube.com/watch?v=DHi5HnIij3Q