Why is the SSL certificate not working (connection is not secure)?

Question

System administration

Moved the site to another machine. On the previous certificate worked fine. Now something warns about an insecure connection.

Answer 1

In this case, the certificate may not work for two reasons:
1. Incorrect configs. In other words - it was not screwed correctly.
2. Changed site domain.

Answer 2

offended

Answer 3

You did something wrong.
PS Sorry, I could not resist, what question - such an answer.
Need more input. What kind of web server, how was it transferred (configs, etc.)