Change boot seq hp p2-1134

I am trying to change to boot seq on my HP P2-1134. The problem is in the boot seq between CD/DVD drive and the HD there is a WD MY Book 1tb USB drive. as a result when I try and boot the system finds nothing on the CD/DVD drive to boot from and so tries for some reason to boot from the USB drive...When it does I get the msg 'INVALID PARTITION LIBRARY" previously I had this message with the...