Eventually downloaded the mobo manual. Keep tapping the DEL key as the pc is starting up, it should go into Setup. Use the R arrow key to move across the main menu sections at the top to the BOOT section, then hit Enter.
Change the boot order so first boot device is the floppy (if you have one) second the CD drive, and third the internal HDD. You don't want to see your ext hdd there.
Press whatever key(s) you need to save the changes and exit.
It should continue starting and boot from the internal HDD