Problem:
Trying to install a new prestashop but getting error 500, the installation doesn’t even start

Solution:
Check file and folder permissions. Folder permission should be 755 and file should be 644.

Commands for changing file / folder permissions in linux through (ssh) console:

This is for changing folder permissions

find /public_html/prestashop -type d -exec chmod 755 {} \; 

This is for changing file permissions

find /public_html/prestashop -type f -exec chmod 644 {} \