Looking at the security warning and your HTML source the problem seems to lie not on your server, but on some of the elements that you are loading from external sites.
For example this image:
http://coinpot.win/assets/img/banners/728x90.gifIt's loaded via regular http, which causes your whole website to show up as potentially insecure. Now apparently coinpot.win doesn't support https, so you'll likely have to host the banner yourself.
There is also an iframe somewhere on your page that loads an external page via http. There might be even more, but I didn't fully look through it.
Word of advice: When loading resources (ie. images, iframe content, css files, js files, etc) refer to the url via:
//domain.com/path/to/resource.gif
instead of
http://domain.com/path/to/resource.gif
This way your browser automatically loads the resources via whatever protocol -- ie. https instead of http -- you are currently using.
Note that if the external site where you load the resources from doesn't support https you'll have to host it yourself -- or choose an external resource that
does support https.