Very strange issue happening here, and I am pretty much out of ideas. Whenever I use SSMS to try to log onto an instance using my Windows credentials, I have no issues. When I try to login using a SQL login I recently created, the login dialog box hangs for a few seconds and then closes like it has made as successful connection, except nothing happens. No error message, nothing. Another interesting note is that the same thing happens no matter what I put into the User Name and Password field. So I could literally just mash my hands on the keyboard for both User Name and Password and the login box will just disappear with no error message. The interesting part is that if I try to log into the instance using sqlcmd at a command prompt, everything works fine. I can connect using the same recently created SQL login and run queries just fine.
I've checked the SQL Server logs and I don't see any errors showing there. I've also confirmed that the server is set to mixed authentication. I've tried running a trace while logging in to see if I could pin down any sort of error, but literally nothing shows there when recreating the issue. I usually get something to show there if there's an attempted login successful or not. The issue originally occurred with SSMS ver 17.1. I've since uninstalled that and re-installed ver 17.3, but it did not help at all. I've also run Windows Update on the server just in case, but that did not help, either. All services are up and running and all network protocols and settings appear to be fine as well.
I'm basically stumped so any ideas would be appreciated.