Insert the removable disk in the removable drive before you start your computer. But in this case, make sure that the first boot device in BIOS is not USB drive, else computer may not boot at all.
1. Log in as Administrator account in windows or any other account with administrative privileges
2. Insert your removable disk into the USB port.
3. Click Start, now right click on my computer and select manage
4. Now, click Disk Management
5. Right click on your removable drive partition and select Change Drive Letter and Paths under Disk Management ( you can find your drive easily through size )
6. Change the drive letter some other drive letter like X: or Z: which is not reserved by some other drive on windows.