A large windows update can result in Avaya Communicator failing to work properly.
Using Windows 'Add/Remove Programs', uninstall Avaya Communicator.
Restart your computer.
Install Avaya Communicator using the install file that is (probably) saved in your Downloads folder.
If the install file is not in your Downloads folder, you can download it from here:
The newly installed Avaya Communicator should pick up your settings and start to operate correctly.
If it does not, check the settings are correct using this article: