Windows – This PC is gone from the file explorer navigation pane and is empty when I view it

One option is to go through the registry but not the way you did it. It should be done by changing the existing key, not by adding a new one. I had cases where the "CLSID"-Number didn't match (maybe due to the windows/Dropbox version, but I'm not 100% sure about it). If this is the case for you, try to find the right key/value first:

• In the registry try to locate System.IsPinnedToNamespaceTree (search for values, not keys or data => see note at the bottom of my answer).

  

  Make sure you start searching at the "root folder" (Computer).

  

• You should find a registry key/value that looks like this:

  HKEY_CURRENT_USER\SOFTWARE\Classes\CLSID{E31EA727-12ED-4702-820C-4B6445F28E1A}\System.IsPinnedToNamespaceTree

  

  Depending on the software you have installed there will be somewhat around 20 or more in total. Make sure you got the one that belongs to Dropbox. Usually there should be some kind of "dropbox-reference" in the registry key. If you are unsure you can search for the CLSID on the internet, it's a unique global identifier.

• Change the data of the System.IsPinnedToNamespaceTree-value to 0

  

Make sure you don't just change the one you created yourself. There should already be one that has been created by the Dropbox installer. And make sure to change all the created keys for Dropbox (with the same CLSID-Number) not just the first one you find. You should find a second one within the key HKEY_CURRENT_USER\SOFTWARE\Classes\Wow6432Node\

If Dropbox has been deinstalled the "data" should remain 0. There might be some process of Dropbox that still gets executed at startup and changes it back to 1. In this case you can remove access altogether to the CLSID-key (right click, choose permissions and select "access denied").

Note: In the registry....

• the "folders" are called keys
• the "entries" in the folders are called values
• the "values assigned to the entries" are called data

Well, I think I found the right registry edit. Before (note that Contacts folder has had 'hidden' attribute set, so it doesn't show in the main pane but is still visible in the Navigation Pane): Here is an after shot: Here's the PowerShell code to perform the edit, it must be run from an Admin PowerShell console:

$FDkey = 'HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\FolderDescriptions'
@(
'{31C0DD25-9439-4F12-BF41-7FF4EDA38722}' # 3D Objects
'{56784854-C6CB-462B-8169-88E350ACB882}' # Contacts
'{1777F761-68AD-4D8A-87BD-30B759FA33DD}' # Favorites
'{bfb9d5e0-c6a9-404c-b2b2-ae6db6af4968}' # Links
'{4BD8D571-6D19-48D3-BE97-422220080E43}' # My Music
'{a0c69a99-21c8-4671-8703-7934162fcf1d}' # Local Music
'{33E28130-4E1E-4676-835A-98395C3BC3BB}' # My Pictures
'{0ddd015d-b06c-45d5-8c4c-f59713854639}' # Local Pictures
'{4C5C32FF-BB9D-43b0-B5B4-2D72E54EAAA4}' # SavedGames
'{7d1d3a04-debb-4115-95cf-2f29da2920da}' # Searches
'{35286a68-3c57-41a1-bbb1-0eae73d76c95}' # Local Videos
'{18989B1D-99B5-455B-841C-AB7C74E4DDFC}' # My Video
) | Foreach {
   $keypath = "$FDkey\$_\PropertyBag"
   new-item -path $keypath -erroraction silentlycontinue
   New-ItemProperty -path $keypath -name ThisPCPolicy -value Hide -force
}
get-process explorer | stop-process

Keith