I had the same problem. I disabled all firewalls and anti-virus software, to no avail. My situation is a bit different, being behind 2 routers and running Windows 10 as a guest machine under Linux, but disabling all that stuff did not work for me. Although i was able to ping and browse various websites, i suspected the DNS was the problem, so i went to Settings->Network->Change Adapter Settings->(right click)Properties->Internet Protocol 4 (in list) and changed the DNS setting to manual configuration, using the DNS server of the first router off the cable (i.e. the ISP DNS); did the same thing for Internet Protocol 6. The "Activation" worked immediately. Not sure why the TT Activation server could not be found using the standard DNS configuration, which works for everything else, but i suspect that they are being a bit too clever with their server. I don't know whether the firewall or anti-virus settings mattered in my case.
