Failed to load https://pecwebmail.com/wp-content/plugins/revslider/public/assets/assets/svg/navigation/ic_close_36px.svg: No ‘Access-Control-Allow-Origin’ header is present on the requested resource. Origin ‘https://www.pecwebmail.com’ is therefore not allowed access.

Your slider is trying to make an AJAX request to that file, but the problem is that it is still using the non-www URL for some assets and by default browsers will not allow cross-domain AJAX requests like this (www vs non-www are treated as different domains).

Since the request fails, this means that the SVG file is not properly loaded, which causes a later part of the slider script — that was expecting the SVG to be there — to fail. This stops the slider loading.

You will need to update your slider’s settings to use the URL with the www. If you’re making this change permanently you should do a search-replace in the database to update the URLs everywhere on your site. This should also fix the slider. See the Changing Your Domain Name and URLs section of the Codex for how to go about this.

NOTE: Please take backup of your site before doing search replace. You can use UpdraftPlus backups plugin to take backup of your site. From there, you can restore the database easily if something goes wrong.

Make sure that you also replace guid

You don’t need to do this. The GUID is merely a unique identifier for RSS, and serves no other purpose. It is not the permalink to the page or post. This is a misconception.

If you change the GUID and a user is using RSS then all your content will appear as new. So unless you’re going live for the first time on a new URL (which OP is not), you should not be changing the GUID.

This article gives a good overview of the GUID and when and when not to change it.