Before I even go further: yes, the "hide empty drives" has been unchecked)
I had to reinstall my machine and I was able to to see the drive letters for the internal flash card reader. However I think something might have gone wrong when I give my external HDD a drive letter that was held by one of the flash card reader).
I wrote "I think" because I am not really sure since I never wanted to use the internal card reader till today so I never noticed there was an issue.
Anyway, the internal card reader does not show up even when I insert a card in the reader. Basically nothing happens. I have uninstalled the "USB Mass storage device" and it gets installed without any issue but the problem is still there: I can't see the reader.
Ironically, the INTERNAL flash card reader has a USB slot and when I insert a EXTERNAL flash drive, the EXTERNAL flash drive shows up.
Does anybody have an idea what could be going on. This is a relatively minor issue and not worth my time to reinstall my machine but it is annoying.
The easiest way to prevent drive letter problems and detection like this is to make sure the only drive installed in the computer at the time of OS installation is the drive you want to install the OS onto. Afterwards, reattach any remaining drives and multi-card readers. Mutl-card readers are usually attached via an internal USB header/conector to the motherboard.
So, unless someone else knows how to resolve this without reinstalling windows, this is the only option I know of to make it work.
I was able to repair it myself. I basically uninstalled the device in the device manager and then I unplugged it from the motherboard. I rebooted the machine and one everything was up, I plugged it back into the motherboard (although in a different port just to be sure). Immediately the folders showed up.