The site was crookedly transferred from hosting to openserver. Missing some elements and other errors. How to fix?

Question

CMS

Good afternoon . There is a site on CMS Joomla. It was necessary to transfer it to the local openserver to change the theme a little. Previously, there was no experience with this cms, so I sit side by side with Google.
But in the end, I stopped already at the moment of transferring the site to the LAN ....
I did everything right:
1. Created a domain in openserver, and threw all the files there
2. Imported myself a database
3. Changed everything that was boring in the configuration file .php
And the site somehow started up .... but
everything that was displayed from the admin panel disappeared (some blocks, menus) + as I understand it, some scripts failed (the same map doesn’t work either.). Tried to go to another page on the main one displays something like "you do not have rights la la la".
Krch a lot of errors and the site did not transfer normally.
What is the reason and how to fix it?

Answer 1

Guys, krch mistake was commonplace. Due to differences in php version ....
The hosting was 5.3 and I had 7.1 ....
But now I'm interested in another question ... .
If the site was written for version 5.3, shouldn't it work in newer ones? I would understand if it was written under 7.1 but did not work in 5.3. What about support and all that? Or are they rewriting everything from scratch each version? Eh, I’d better go further with banal layout, otherwise it’s not far from questions of the “meaning of life”.

Answer 2

Most likely because of this, although I could be wrong ...

Depending on the PHP version, two or three different PHP APIs can be used to access the MySQL database. The following extensions are available in PHP 5: deprecated mysql, mysqli and PDO_MySQL. In PHP 7, the deprecated mysql extension is not available and only the last two are left.