If you are encountering a WordPress error message or white screen then don’t panic below are some basic errors and there solutions you can check it here.
The white screen
Due to PHP errors or database error this problem can arise. Due to this you can’t able to see anything you just able to see a white screen.
A plugin causes conflict:-if one plugin is conflicting with other plugin then you may get this type of blank screens. You just have to make disable all plugins and again reactivating plugins one by one.by this way you can check the plugin conflict. If you are not able to login or access your admin panel then just go to wp-content/plugins and rename the plugins folder as plugins_deactivate. This way you can able to de activate all your plugins at a time.
Your theme may create such problem:
If you are having the blank screen after activating a new theme then you have to deactivate that theme and activate the default theme and check what the problem is. If you are not able to access the admin then go to wp-content/themes/ search for the active theme name and Rename the folder for the active Theme.
Internal Server Error
This may comes for different reasons like
Issue may come due to miss configured .htaccess file. Just find your .htaccess file and rename it to .htaccess_old.
Go to Settings > Permalinks and reset your permalinks. This will create a new .htaccess file for you.
Check your wp-config settings.
Deactivate all your plugins and check is there any issue for plugins
Activate the default theme and check is there any issue for theme or not.
Try to re-uploading the wp-admin and wp-includes folder from a fresh installed WordPress folder. First check both the WordPress versions should same.
Error establishing data base connection
/** MySQL database username */
/** MySQL database password */
/** MySQL hostname */
Try to reset your MySQL username, password again create that and give proper permission and try again.
Try to contact with your admin provider for database details.