It could be recognized by your computer but not assigned a letter. If this is the case then you can assign a letter by right clicking on My computer, manage, then near the bottom of the window find disk management. In the bottom section you will find all of your recognized drives, if your flash drive is there then right click on it and assign a letter. If your drive isn't listed in disk management then the best advice I can give is to restart your computer, unplug your flash drive, and/or plug your flash drive into another computer and see if it works there.
I sure hope that you can get it all sorted out, I know what a pain these things can be.