I'm having the same problem too, but with Windows 7. Pressing or holding del, as the manual says, does nothing or will take me to the Windows boot options screen from which I can only select repair tools or load win7.
I looked around but I can't find any solid answers. Some say to hold down multiple keys to force an error, some say to press most keys such as f2, f8, del, ins, etc. Nothing works.
I put a user password in the bios, so maybe thats interfering. I have a cheap, but perfectly functional, usb keyboard directly connected to the mobo.
Asus maximus vii hero rev1.01