Before trying that, which takes a serious amount of time and effort (and doesn't always work), try the following.
It is possible it is the USB and also the way the data was put on it. You might want to try putting it on a different USB and see if the computer will read it. I have had that issue before. Some brands just don't like each other. You could check with Toshiba and see if there is a preferred USB brand that works with their motherboard.
Also, if it was just 'copied' over then it may not recognize it. You need to actually have it burned on the USB drive. Here is a link to a program that can do that (burn it to the USB)... http://www.isotousb.com/ .. of course there are probably others out there as well.