Please help! Can't log in as admin.

It sounds like you aren’t using a valid SSL certificate. You’ll need to contact your hosting provider, or the certificate authority you purchased it from, about that.

Meanwhile, access your database via phpMyAdmin (usually found in your hosting account’s control panel) and change your siteurl and home values back to http directly in the database following this guide: https://codex.ww.wp.xz.cn/Changing_The_Site_URL#Changing_the_URL_directly_in_the_database

There are other options covered at https://codex.ww.wp.xz.cn/Backing_Up_Your_Database besides cPanel. cPanel is just a very common hosting account control panel.

Almost everything covered there won’t require you to access your site to backup your database.

Everyone offering support here is a volunteer, so we don’t offer support outside of these forums, but your hosting provider probably does and can probably help you further. If not, please try http://jobs.wordpress.net/ or http://directory.codepoet.com/ and do not accept any hire or direct access offers posted to these forums.

You’re welcome!