Try thumbdrive in a 2nd computer.
1) Does 2nd computer allow you to see files, if No then
2) does it show up under my computer, if so right click on the drive and check properties. Are the properties correct (Correctly showing the size) and that the drive is formated.
3) If drive shows up under my computer but can not access files, try to format the drive (All data on drive will be loast).
4) if dive does NOT show up on a 2nd computer, then it is time to buy a new thumbdrive. Order from Newegg, cheaper than downtown bestbuy.