There are situations where signing in to the locally installed Teams App does not work at all or does not work as usual.
Take the following steps to wipe the local possibly corrupt Teams data and synchronize a new copy from the server.
Login to Teams online https://teams.microsoft.com/ succedes and you can work within the web client. (If not, there is a problem with your account and the following steps wont solve your issue.)
Reset Local Teams Client (Windows)
- Close Teams completely.
To do this, click on the upward facing arrow in your task bar, right click on the Teams icon and choose "Quit".
- Open a new File Explorer window and type "%localappdata%" (without the quotes but including the % caracters). Press the Enter key.
The path you are sent to can vary depending on your system, but usually looks like C:\Users\<username>\AppData\Local
- Open the folder named "Microsoft".
- Delete every folder whose name begins with "Teams".
- As in step 2 enter "%appdata%" (once again without quotes but including the % characters) into the address bar and press Enter.
This path too can vary but usually looks like: C:\Users\<username>\AppData\Roaming
- Delete the folder "Microsoft Teams"
- Open the subfolder "Microsoft".
- Delete the folder "Teams".
- Finally open Teams.
If your Teams App cannot be found, download it again and reinstall it.
- Sign in to the online Teams Application https://teams.microsoft.com/, click on the profile picture at the top right side of the app and click the "Download the Desktop App" link.
- Save the downloaded file.
- Doubleclick the saved file to reinstall Teams.
Reset Local Teams Client (Mac)
- Quit Microsoft Teams.
- Bring Finder to the foreground and open your "Library" folder. To do so, open in Finder the menu "Go", keep the Option-(Alt-)Key pressed and chose the menu item "Library".
- Open the subfolder "Application Support" --> "Microsoft" and delete the subfolder "Teams".
- Finally restart Microsoft Teams.