Esc k7s5a will not boot to dvd

My k75sa will not boot to dvd. It boots fine to cd and I have checked my dvd (it is windows 7 rc) and it boots fine in my other system. Anyone else had any experience with this problem and/or have a solution? Is it the burner, motherboard or bios? I haven't tried swapping out the burners yet.

I have two dvd drives in the esc k75sa: one is a dvd rw and the other just a dvd read. The dvd rw is the master on the secondary IDE channel. This is the drive I use to boot from CD. I can boot my winxp install disk (which is CD) but it will not boot from a dvd disk. ( I also have another computer, in which the dvd boots fine - thus I know the dvd disk is okay.) In fact, when I boot to winxp install disk, and use repair console to look at the drives, if I put a CD in either of the dvd drives it can read both, but can read neither if a dvd is inserted.