don't know if this will help:
IT might be that the sharing tab is simply not enabled properly as an extension.
download ShExView:
http://www.nirsoft.net/utils/shexview_setup.exeInstall and Run it.
Once it loads, look for an item titled "Shell Extensions For Sharing"
If it's Disabled- Enable it.
If it is already enabled, Right click, and select "properties" (Not "File Properties"). the third item from the bottom, titled "File Extensions" should read "Directory, Drive"
In this case, it sounds like yours might only read Directory.
If it does only say "Directory"- try this:
Open Notepad and paste the following:
Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT\Drive\shellex\PropertySheetHandlers\Sharing]
@="{f81e9010-6ea4-11ce-a7ff-00aa003ca9f6}"
Select File-Save and choose File Type "All Files(*.*)" and save it as a .REG file- for example, "sharedrive.reg"
Locate the file on your desktop or in an explorer window and double-click to merge the contents.
IF you still cannot see the sharing tab for drives, try rebooting.