No drive letter assigned to USB drive on windows 8.1

As we found out through the comments the problem may be solved using Windows' diskpart. Obviously the Linux tools somehow created a MBR and/or partition table Windows couldn't read properly (or had some other issue with).

If you're using these instructions, do so with care! Making mistakes might mean you're losing all data on one more more disks. If you're unsure, let someone else who's more experienced do this!

  • Open the start menu and type diskpart. You should get one hit, launch it and confirm the UAC prompt in case you're asked.

  • Wait for the console window to show an input cursor (flashing horizontal line behind DISKPART>).

  • Type list disk and confirm with Return.

  • Locate the disk you'd like to format/reset. Double check you pick the right one. Remember its number (listed under ###) for the next step.

  • Now type select disk # where # is replaced with the number from the last step.

  • Once again type list disk and the correct disk should be marked with a * in front of it.

  • Type clean, confirm if asked and wait for the operation to finish.

  • Leave diskpart using exit.

  • Windows Explorer should now ask you what to do with the uninitialized/empty disk. If it doesn't, have a look at disk management (open the start menu and run diskmgmt.msc). You should find the uninitialized drive and be able to create new partitions and format them.

I had exactly the same issue and the Mario's solution did not fix my problem. Additionally to Mario's solution do the following:

  • after 'clean' do not leave diskpart using 'exit'
  • type 'create partition primary'

This will create primary FAT32 partition (which was not possible from the Disk Manager as described in comment of 'Stanislav Mamontov' to Mario solution). This partition will be recognized, directly mounted and available. Now you can reformat to e.g NTFS if needed.