Missing Data on Index.php

Having a problem with new installation using Default theme.

wordpress installed to this folder = https://www.mydomain.com/main
blog url = https://www.mydomain.com

index.php at blog url returns the default theme plus shows “categories” in sidebar, but when you click on the category name the server returns a server config error (no #). There are no posts listed on the page (including the “Hello World” post.

The category links for example are searching for:
https://www.mydomain.com/category/category_name … but only returns an error.

I’ve checked MySQL and the posts and cats are listed. I have .htaccess file on root.

Any help would be appreciated.

Lyle