I will change my boot device on my dimension 8400.Ok,i press F12 at start-up and selected the first "onboard or floppy drive" and then enter.But i can,t change it.I got the message: "selected boot device not available".And then i stuck,and can,t do anything.Except ctrl alt del.

What do i wrong?How can i set the first device to my dvd-rom?

Oh yeh,i have a floppy.