does it show up under disk management sometimes devices loose their drive letter for whatever reason. Try a diffrent USB port and a diffrent computer if all of this fails it is quite possible it is dead.
Have you tried to test it with SeaTools for Windows? http://www.seagate.com/support/downloads/seatools/
This tool always can check whether it is the problem of your USB drive.
For the inner data, I think you can firstly try a USB drive recovery freeware that can normally retrieve your inaccessible data back as long as you have not rewritten it. Since it is free, you have no need to worry about the money problem. Just take more chances to get your data back: http://www.freeware-fix.blogspot.com/2013/02/usb-drive-...
In the future, you should keep at least two copies of everything important on separate drives in case of similar problems.