Yes, we have our own Tech Discussions board for TS3 but I see this thread got moved to TS3 General instead which is okay too.
The best thing to try, if changing the password doesn't help, is to clear your Internet Explorer's cache and cookies, being sure to deselect the option to retain data for Favorites. Even if you never use IE as a browser yourself, and even if on Win 10 and it's hiding on you, IE has to be in there someplace and the game (TS3) uses its resources. This is a very common problem with cookies and the user id/pw combo.
For a visual: https://kb.wisc.edu/page.php?id=15141