After an SSL installation on your web hosting account you may not be able to open your site.
This issue is caused by the SSL installation which requires a DNS change of your domain's A record. Right after the SSL installation you might be still resolving your domain with the old DNS settings. Generally those changes should occur immediately but it is still possible to access your website using cached DNS information.
You should allow a few hours for the DNS change to propagate and take effect. After that you will be able to access your site without any problems.
It is also a good idea in such cases to clear up your browser's cache and your local DNS cache.
If you are having problems with your SSL certificate, ask your host for assistance.