If you have tried with another browser and another pc I can’t think of any other check to do without knowing more information about the system installation.
Maybe, if you know, you can use the browser dev tools (pressing F12 and see Network tab) to check the request and response made during the login process (call to http://…/api/vi/auth) but I doubt it will provide us with more information…
Talk to the Taiga instance administrator. I don’t think so, but maybe for some strange reason your user is blocked.
