Quote Originally Posted by arxvaldex View Post
I am having difficulty using any other PHP version than the ancient version 5.4
If I select any other version above 5.4 such as 7 all the way to 8.1 my site does not load at all (blank site without any error message)

Zen Cart Version 1.5.6c

In my cPanel I can set the PHP version in this menu:

MultiPHP Manager

System PHP Version
The system default PHP version is set by the system administrator.

Any domain that is set to the inherit value indicates that it does not have its own PHP version explicitly set. Read more about inherit.

Set PHP Version per Domain
Select the domains that you wish to change from the table, then apply a PHP version from the list.

Any help will be appreciated
That's definetely an old version. Have you checked your store/log directory to see what error messages are being written to the log files? That will usually indicate exactly why the screen is blank and help you narrow down the issue.

It's probably some outdated PHP function that is still being used by your older site but has been deprecated in more current versions.