Do you firstly use this pen drive on your computer?
Sometimes, a new drive need a compatible driver to boot as it is firstly used on a computer. Just download a driver for it: http://www.toggle.com/lv/group/view/kl40616/Driver_Pen_...
If you do not use it firstly on this compute, have you tried to assign a new letter to this drive in “Disk Management”? http://support.microsoft.com/kb/307844
At last, if all these ways above don’t make a sense, you may have to use a free drive recovery tool to regain your data and format this drive afterwards. Honestly, my friend has found this freeware in this forum and successfully tried it to recover all his inaccessible data back. So, you could give it a shot: http://blog4mark.blogspot.com/2012/11/how-to-repair-cor...
I hope this helps.
Have you tried different ports? Maybe a different computer? If a computer does not see the device even to the point of the new hardware detected message, you need to bring the thing to a computer repair shop to see if they can fix the connections and maybe the electronics. The data on the drive is probably fine, but you need to fix the USB connections.