Have you already attempted performing a factory reset on the TV? You can follow the directions in the link below.
Just went through this problem, got a solution that worked for me. The message that I got on my KS8000 TV when I tried to log the TV into my Samsung account was "unable to reach server, update firmware to fix this" or close to that. I already have the latest firmware from a recent manual update, so that wasn't the answer.
Tried to find and install the "Smart Things" app. Couldn't even find the app, so that was a dead end for my TV.
Called Samsung support, and they had me go through the Settings -> Support -> Self Diagnosis -> "Reset Smart Hub" path. If you follow that all the way through, you'll find that you can log into your Samsung account again. You have to do some more setup that's not relevant to logging in, but not much.
Try reconnecting to the internet. It's a shame that Samsung passes the buck on helping customers... If you're goint to act when people need help on a Samsung product, then you need to advertise that you won't help when we BUY IT. A big RED sign: "If you but this model TV, made in sweatshops by 4 year olds in China, at this American store, you will not receive support. Thanks, Management."