Fatal error: Call to undefined function wp_json_encode() in D:\Hosting\3647649

I too am not a programmer, but the key thing here for you to do is bring your WordPress site back to as default a state as humanly possible. That said, first thing I would do is deactivate ALL your plugins. Of course, being that you cannot access your site that task can be a bit tricky. But, never fear, there’s a link here that will help you deactivate your plugins without the need to access/log in to your site:

https://www.wpbeginner.com/plugins/how-to-deactivate-all-plugins-when-not-able-to-access-wp-admin/

Once you’ve done the above, and if the issue continues, then I would also switch your theme to a default (e.g., Twenty Fifteen) theme. To do that, go to the following link and follow step 3 entitled “Move the theme”:

https://themefuse.com/restoring-wordpress-after-a-crash/

Beyond this, if things still do not work, then I would simply reinstall WordPress. In fact, some wiser than I folks here might say, given your error message above, that’s the first thing to try. To reinstall WordPress, find the “Manual Update” section on the following link:

https://codex.www.ads-software.com/Updating_WordPress

Hope this helps!