We received one of the Toshiba L855 models in to the shop for depot repair.
It was difficult to find any pages about how to boot a toshiba L855-S5405 to CD, but eventually we found it. The procedure to boot the laptop from a CD is to hold the F12 button and then press the power button. Continue to hold the F12 button to boot a toshiba L855-S5405 to CD and you’ll be in business in no time.
Hope this helps someone out there.