Vostro 3560 - Can't change boot device

I have a problem when selecting a different boot device with F12 on startup. I want to reinstall my system with linux mint 17 (currently 15) but with the disc in the dvd drive or with an bootable usb stick i'm unable to select these to boot devices in the menu..

This is the setting i currently have enabled and the only boot device listed is the harddisk

http://i.imgur.com/FH8uG7x.jpg

How can i solve this problem, so i will be able to boot again from dvd and/or usb so i can reinstall my system?

Thank in advance!