If drive letter C is not getting assigned to windows partition on your system having only one windows partition, this might create issues when you connect an external device having multiple partition. Let us know if you encountered any other issues other than with external devices.
The cause of this problem may be due to software you might have used to make a bootable USB.
Or might be due to some other partition on the system which is flagged as boot parition.
This flag causes windows to assign drive letter C to this drive and the drive you install windows gets subsequent drive letter. Say for instance, you have a system with one hard disk with two partition and one CDDVD drive. Then if the second partition have a ‘boot’ flag, it will get drive letter C. CDDVD drive will be assigned drive letter D. Then the partition you are installing windows on gets drive letter E.
To overcome this problem you will have to unflag the ‘boot’ flag from other partition.
Assuming you dont have any working operating system on your system.
We suggest you to use GParted after running Ubuntu live CD.
Once you have removed the boot flag from other paritions, you can install windows and the partition you install windows on will get drive letter C. Once your windows is installed you can connect your external device and all the partitions will show up.