Doesn't show in "My Computer" or "Disk Management"?
How does it show in "Disk Management"?
You perhaps need to change a new letter to this drive in "Disk Management":http://technet.microsoft.com/en-gb/library/cc757491%28v=ws.10%29.aspx
If unfortunately, that ways doesn't make a sense, I know there is a free USB drive recovery tool
that generally can restore the inaccessible data from a drive and a memory card You could try it here: http://www.freeware-fix.blogspot.com/2013/02/usb-drive-not-recognized.html
From now on, you should remember to keep your data backed up all the time.