Installing Windows 7 on iMac via external superdrive resultes in "No bootable device-insert boot disck an dpress any key".

I previously had Windows 7 on my Mac, but removed it after returning from deployment because it had a virus that I could not remove.  The only way to remove was to insert a CD/DVD with the anti-virus on, but in my absence, the optical drive was not cleaned and did not work. I had only been using partition for college, so I removed it. 
Now, six months later I am trying to re-instal Windows, but after creating the partition and inserting the disk into the external Superdrive, when Bootcamp reboots I get "No bootable device -- insert boot disk and press any key".  Nothing happens, I can't even type on the screen.  I can reboot to Mac via the alt-option key fine, and I can see the drives, the Windows CD, etcetera, but nothing works.  When I go back to Mac, Bootcamp won't work unless I delete the partition over from scratch, but I'm getting the same result.
Is the computer looking for the internal optical drive (which doesn't work, and can only be repaired by sending the whole thing back to Apple)? Is there a way to default to the external optical drive?

Bob, thanks.  I misread the PDF (font on phones is difficult to see).  Got it fixed now.