Quote Originally Posted by szlamany View Post
Maybe you have conflicting SQL services running, that you had previously managed to stop and clear up, and all that re-booting got them START'ed up again. Go into SERVICES and see what you have for instances. If you have two express versions, they cannot BOTH listen on 1433 - you have to change ports. Also, sometimes those ports are selected dynamically - you should be able to see the port in the IP setup.
Wouldn't this be an issue on S, not an issue on A?

One thing to note is that the code shown in post #1 will show two instances of SQL Server, the 2012 version and the 2017 version. B connects to the 2017 version either via the program or via SSMS (I haven't tried connecting to the 2012 version). A sees both versions, but won't connect to either. I'm actually a bit surprised that neither A nor B sees more than just the two on S. I thought it was the case that VS installed a version when it installed, and both A and B have VS on them. Perhaps VS stopped doing that after some version, but A has both VS2010 and 2019, though I believe B has only VS2019.

In any case, it was an eventful morning. I decided to test out what TG was saying in a plodding, deliberate way. I shut all three computers down last night, so the first thing I did was start up S and A. A wouldn't connect. I then started B, which did connect just fine. That was test #1. I then shut down all three, again, and shut down the router, as well. After all, something DID happen where I lost internet a bit mysteriously, for an hour or two Sunday. I don't know whether that was related, since I hadn't been using S during that time (though S was on, at the time). However, S couldn't see the internet after that until I rebooted it, as noted in post #13. So, I had some hint that the router might be related.

Once everything came back up, neither B nor S could connect to wireless anymore. A was fine because it's on an ethernet cable. This took a long time to work out, including a fair amount of time on the phone with the service provider. Eventually, they did solve the problem, though they also didn't quite identify it. The solution was to change the WiFi network password. This got B and S back on the network. Of course, you don't put in a password every time you connect to your home wireless network. The computers remember it, and since both B and S managed to lose the password at the same time, I can only assume that it was the router that actually lost the password. The password did show up in the router settings, but it's a doozy of a password, so if one character had been dropped, I likely wouldn't have noticed it.

The new password is 14 characters, symbols, numbers, upper and lower case, but when I connect with B (a Surface Pro 7), it is saying that I'm using an older security protocol which isn't totally secure. If I look at the connection, it's WPA2, so I don't think it's all that insecure.

In any case, after all that, I was back to where I started the morning at: A, B, and S are all on the internet. B can connect to S via SSMS or the application. A can see the two SQL Server instances on S using the code in post #1, but can't connect using either SSMS or the application. Also, all three were fine the last time I tried them, which was perhaps as far back as the 29th, which date I only know because that's the last time I had posted in this thread. I may have used the system a day or so after that, or maybe not, but it WAS working then.

I'm still not 100% confident in the router, but aside from the inability to connect to SQL Server, that's the ONLY issue I'm seeing, currently. I'm not seeing how the router could be impacting that.