Published custom post could not be found when viewed

Hello!
I have been following lynda.com tutorials for child themes, custom post types and custom taxonomies, I did them correctly as far as coding can go.

But when I was done with my custom posts and taxonomies, I published my post, it had an URL, but the wordpress couldn’t find it or couldn’t load it, it said

“Not Found

Apologies, but the page you requested could not be found. Perhaps searching will help.”

It is now beyond my knowledge on how to fix this. Everything works fine except viewing a published post.

Please let me know what code I should post. I recently made a child theme php file, functions.php and posttypes.php.