|In BIOS it would be best to set an optical drive as your first priority then your OS drive as your second.|
The suggestion in #2 above is a good one to follow.
In days of yore it was the standard to set boot order as floppy, then HD; then when cdrom arrived - floppy, cdrom, HD.
Nowadays for whatever reason (and with the demise of the floppy) many systems arrive HD, then cd/dvdrom boot order. My PC systems are set to cd/dvd, then HD. On Mac systems it a little different (I haven't yet found the equivalent to the PC bios option re' boot order). Thus one holds down the option key as system starts up and then chooses what you want to boot from - if not the default HD.