Issue with functions.php and other issues

Hello

I recently made a mistake, while I tried to install a child-theme on filezilla. I am not completely sure what happened – I retrace everything I have done – but could not remove the Server Error 500 on my site.

So I did a complete reinstallation of wordpress from start and then added a backup. Same issue, except if I pressed reload the site would show, however I could not login in to my backend at all.

Then I change WP Debug from false to true and it showed that there was a issue with the theme that I had. I removed the theme, but it still shows an error. What is worse all my other pages shows up as a blank pages, which It had not done before.

However, now I can login in to my backend.

It shows the following error:

Notice: The called constructor method for WP_Widget is deprecated since version 4.3.0! Use
__construct()
instead. in F:\Domains\Guide002\bloemfonteinguide.co.za\wwwroot\wp-includes\functions.php on line 3624 Notice: The called constructor method for WP_Widget is deprecated since version 4.3.0! Use
__construct()
instead. in F:\Domains\Guide002\bloemfonteinguide.co.za\wwwroot\wp-includes\functions.php on line 3624 Notice: The called constructor method for WP_Widget is deprecated since version 4.3.0! Use
__construct()
instead. in F:\Domains\Guide002\bloemfonteinguide.co.za\wwwroot\wp-includes\functions.php on line 3624 Notice: The called constructor method for WP_Widget is deprecated since version 4.3.0! Use
__construct()
instead. in F:\Domains\Guide002\bloemfonteinguide.co.za\wwwroot\wp-includes\functions.php on line 3624

If anybody can help, I would really appreciate it. Even pay if you can get it to full working condition again.