Waqas

You say that three plugins are safe and the other 3 have problem. Of the ones you listed my suspicion would be on the Lightbox Gallery plugin as that has something to do with Media files. Are you sure that turning the other 2 also causes problems?

The Lightbox Gallery plugin (https://www.ads-software.com/plugins/lightbox-gallery/) seems a bit old – maybe replace with an equivalent new plugin or ask the plugin author for support

The code you have posted still does not seem to show any closing li or ul tags

Yes if you rename the folder then it will get deactivated

Rename the current plugin folder to plugin-old and create a new empty plugin folder. See if that brings the menu back.

You have started the ul and li tags but not ended them. For example:

<ul class="headersocial">
<li class="fb"> </li>
<li class="tw"> </li>
<li class="gp"> </li>
</ul>

It is loading fine at my end – so it is likely a ache issue – why not try a browser you do not use normally?

I believe you have commented all your child theme style code!

So remove at the start it should be:
/* =Theme customization starts here*/

And remove the */ at the end

Why not try this to login:
https://kristincolumbus.com/wp-login.php

Why not try to reinstall WP (just overwrite the wp-admin and wp-include folders with the latest version)

Here is an alternate DIY way. Install this plugin:
https://www.ads-software.com/plugins/simple-custom-css/ (you could go to Plugins in the left column of the dashboard and install from there by searching the WP repository for “Simple Custom CSS”).

After the plugin is installed AND activated then in the Appearance section of the Dashboard you will see a link to Custom CSS. Click on that and paste the code:

h1 {
    font-size: 36px;
}

Hit save and you should be done.

Create a new page template that has a custom loop to show the posts (use Wp_Query) – then create a page called “Blog” – set the slug as blog and apply that template on that page.

I believe the above is the safest approach as other approaches may mean messing around with permalinks and that may change URL of existing entries of the site

Remove the ones that are in the header.php file. Only keep one copy (either in style.css or custom.css – I suggest keep it in custom.css)

Can you also try changing to the default WP theme and see if that helps?

If you have backups then compare the entries for the table wp_users to see if there was a change during the time period you mention

I believe that you did not correctly change all the URL in your database. There are 2 entries in the options table (site_url and home_url) – but that is not all. A number of entries exist in the different tables and you better go about changing all of them. Remember that WP stores a lot of data using serialization. Therefore you need to run something like the script here: https://interconnectit.com/products/search-and-replace-for-wordpress-databases/