Your pendrive cannot be formatted? You can download a software to format your pendrive. Instruction steps :
1 - Click here to download the software in zip file format.
2 - Use 7zip or Winrar or Winzip to open it.
3 - Copy the SP27608.exe file to your pendrive.
4 - Double click on the SP27608.exe file in your pendrive to install it to your C: drive in your computer. 
5 - On your computer, open/run the software to format your pendrive. (Don't choose quick format).

I did try to use this software to format my 64gb and 32gb pendrives, and it works!!! Hopefully it works for your pendrive.