The Problem: You plugged in your USB flash drive. It didn't mount.
Unfortunately, this is a last ditch attempt at getting your drive to mount. If there's something truly wrong with either your USB port, or your USB drive; this guide will not help you.
That said; maybe your drive's contacts are dirty. No, really!
The Solution: A rubber eraser and/or cotton swab with alcohol.
If your drive's contacts are exposed and seem clean to the eye; take a cleaned rubber eraser and rub it across the contacts until they look shiny and clean. The rubber will remove almost everything that comes between your drive and your computer's port.
If your drive's contacts are not exposed, or you have a lot of gunk built up on the contacts; use a cotton swab with a bit of isopropyl alcohol to clean the contacts.