Windows Explorer will not show any (usb-flash/external HD-) drive with the letter H. The drive is recognized by Windows: it does show up in Disk Management.
What I did, months ago, is delete (merge) a hard drive partition - drive letter assignment of this partition was H.
Apparently the H-assignment got lost somehow somewhere.
The practical issue is: whenever I use a usb stick, Windows assigns the first available/free drive letter - which is H. I then have to go to disk management, change H into some other letter, after which the usb stick show up in Win Explorer.
Tried my best to find a solution for this. Wasn't lucky.