Unable to access USB harddrive/pendrive through windows explorer?

I faced this problem once, found out a way and faced it few months later again on another machine. Had to re-discover it this time. Hence this entry, so that I (or whoever can read this) need not re-discover the solution.

Problem:
* USB Harddrive or Pendrive is plugged in.
* Windows recognizes the USB mass-storage device.
* But, unable to access it using a drive-letter from Windows Explorer or Command Prompt.

Solution:
* Open "Disk Management MMC" - Start Run diskmgmt.msc.

* Right-Click the USB drive (disk other than the permanent drives) & select 'Change Drive Letter and Paths...'

* Add a drive letter.

That is it. You now see the drive letter in Windows Explorer.