WordPress site problems can have many causes, but even so, a few basic steps will help you catch most of them. Here’s how to troubleshoot WordPress sites in 60 seconds!
When troubleshooting WordPress issues the easiest thing to check for is a theme problem, so first activate a different theme. If the issue goes away you’ll know it was a theme problem. If not, keep searching.
Next deactivate all the site’s plugins. If the problem stops now you’ll know it was a plugin problem, so turn each plugin back on, one at a time. When the issue comes back, you’ll have identified the plugin at fault.
And if it’s not the theme or plugin, try upgrading WordPress or replacing its core files. If something's wrong with the WordPress install itself this should solve it.
If none of the above works then contact your host and ask them to check their logs to see if something’s wrong on their end.
A Bit More Detail
Learn more about troubleshooting WordPress.