This means the resource could not be found, whether it be a page or an image. This could be caused by an incorrect link, or the file really is missing.
This is a generic server error code. Inspecting the logs can help to diagnose this issue.
JavaScript errors can be caused for a whole bunch of reasons. Chrome DevTools can often help you find the offending bit of code.
Has a theme or plugin not installed properly? This may be due to mismatching WordPress or PHP versions.
WordPress can have trouble connecting to the database if it is down or if credentials are incorrect.
SSL Certificates secure and encrypt web traffic. They may not be configured correctly resulting in an error.
There are a number of reasons for a website to be performing badly. We know various tricks to speed up an old site.
For all the good the web brings there are some bad actors on it. Are you getting overwhelmed by spam? Try using Google's reCaptcha on comment boxes.