At step 4 the tool uninstalled and re-installed Office365.

The Office365 Online repair tool was used.

On the affected user computer the firewall and antivirus were disabled but that made no difference.

Skype for business was working properly and the only change made was the installation of the Microsoft Teams 'crAPP' - rant begins - The same 'crAPP' that everybody is praising because it can blur your background (bah!), but doesn't allow to be installed for 'all users' in the 'programs files' directory and doesn't provide a secondary ringer device option - rant ends.

If the affected user runs Skype for Business from another computer, he can make and receive calls without problems.

When other user with Skype for Business tries to 'skype call' the affected user, the unaffected user hears one ringtone and then quickly the busy tone and the error message 'Call cannot be completed'.

Typically when you place a call you can hear the ringtone while waiting for the other party to answer but for this particular case nothing happens, no sound, nothing.

When the call is placed the window opens and it just hangs in there saying 'calling' but nothing happens.

Problem is that cannot make or receive 'skype (for business) calls' to/from other Skype for Business users, either internal or external.

Text chat is working just fine, including sending and receiving images and desktop/screen sharing.Have an user with Office365 E3 subscription running on a Windows 10 (1809) computer updated with latest patches and drivers, where his Skype for Business has become somehow corrupted.

How to open skype received files