After installing Windows 10, I found that the Volume and Network icons were missing from the Notification Area, and that right-clicking on a Taskbar Icon (eg Word or Powerpoint) did not give me the list of recent files or pinned files I had come to expect from Windows 8.1
Something else I noticed was that my E-MU 0404 PCI sound card no longer worked. That was a shame, but I've been using a USB sound card (AVID Fast Track Solo) instead recently so I decided to remove the E-MU card and uninstall the software and drivers...
When I re-booted, the volume icon appeared, along with the Network notification, and all the task bar icons worked properly.
So it seems that my non-functioning E-MU 0404 card had been blocking something in the system. Weird. Glad it's sorted though.