I don't know why I got "not ready, please check your connection" at the bottom of my "TeamViewer" window, with a red dot, when I tried to sign in I got a checking proxy message.
I used TeamViewer many years ago, but did not seem to have this kind of problem.
Are you sure the computer you have installed TeamViewer on has a fully functional Internet Connection? If so, possibly a firewall or other 3rd party software is preventing TeamViewer from communicating with the TeamViewer server.
Please read the following:
TeamViewer is designed to connect easily to remote computers without any special firewall configurations being necessary. In the vast majority of cases, TeamViewer will always work if surfing on the internet is possible. TeamViewer makes outbound connections to the internet, which are usually not blocked by firewalls.
However, in some situations, for example in a corporate environment with strict security policies, a firewall might be set up to block all unknown outbound connections, and in this case you will need to configure the firewall to allow TeamViewer to connect out through it.
TCP/UDP Port 5938
Can you confirm that those ports are open and available on your network and your computer?