|Whatever you do - do NOT try writing to it... As Derek suggests try it another computer; and see if it shows up as a device/drive in windows Explorer or MyComputer...|
Also try it in more than one usb port on the computer(s) as occasionally one port may not respond to the device being there.
Whenever you wish to remove a usb flash drive... use the eject usb device route (bottom right hand corner); or right click on it and "eject it" in /windows Explorer etc.. Never simply pull it out of the usb socket as that frequently can cause the drive to crash (and you lose the contents.
Hopefully when you do regain access to it... immediately copy the contents to a DVD; and make two copies... DVD is much better for long term storage than any flash drive. The latter are meant really for short term storage and porting data about in a small convenient form. If you have an external hard drive too - then copy them there as well... Label your DVDs and store in a safe place...
What make and model computer do you have?