I find it odd that toshiba would be able to block you from installing it, like I said earlier I have done slack/ubuntu/backtrack on my toshiba satelite a200 th7, I just could not get it to work off of a cd or dvd had to use usb.
Perhaps you should remake the bootable usb and try again maybe there was an error in the making of it. If that does not work I don't know how to help you.
Sorry I can't be of more help too you