If you are having problem with your WordPress, don't waste your time with searching the how to fix or don't harm your website. I did face and still facing with that kinds of issue everyday and fixing them easily. If you have any other problems that is not written below, contact me first please. Finally if I find out that the problem is hosting/server based I tell you what your hosting company should do to fix the issue. I need your Wordpress admin details and/or ftp and cpanel/directadmin etc. panel information according to the error.
Returning 404 Errors of posts and pages
Blank menu problems
mail sending problems
admin problems (Lost password etc.)
file upload problems
Contact Form problems
http error (Image and Media upload)
WordPress 500 internal server error
Installing theme to your website as it is on demo.
Wp 4.5 wp-includes/functions.php on line 3608 (or other lines)