The key to press to toggle the choices of startup media is [F12] on the Toshiba laptop, series 5205-S705. For example, if you want to boot by CD, you press [F12] and then use the arrow keys to go [right] by a couple of icons, and then [Enter] to select the icon that looks like a single CD disk.
The [F12] must be pressed very early after power on, otherwise the default media will start to boot the operating system, e.g. internal hard disk.
You can use this feature to boot from the second internal disk (in your style bay, if you have one).
I have never been able to boot from USB devices on this laptop.