won't install

Please install the health check plugin and verify your site runs on PHP version 5.3 or greater. https://www.ads-software.com/plugins/health-check/

If it is not. You need to contact your hosting provider for them to upgrade. PHP 5.3 came out in 2010

thank you David
The health check says:
“Excellent: Your server is running PHP version 5.4.27 and MySQL version 5.5.37 which will be great for WordPress 3.2 onward.”

Anything else you recommend?
thanks ??

Sounds like a plugin/theme conflict.

To test for a theme conflict:

1. Activate default Twenty Ten, Eleven, Twelve, or Thirteen theme
2. Check to see if the issue still occurs
3. If the issue does not occur after having activated the default “Twenty” theme, your theme is causing a conflict with landing pages.

To test for a plugin conflict:

1. Deactivate ALL plugins
2. Activate Landing Pages
3. Check to see if the issue occurs

If the issue does not occur, one (or more) of your plugins is causing a conflict with Landing Pages.

To determine which plugin(s) is causing the conflict, follow these steps:

1. Activate each plugin one by one
2. Check to see if the issue occurs after each plugin is activated

I get a blank white screen on the site as well as the admin page, so I cannot activate or deactivate anything. What to do?

I’m running WP 3.9.1 MultiSite. Is the plugin compatible with WPMU?

Do this https://www.inboundnow.com/what-to-do-if-a-wordpress-plugin-breaks-your-site/

Then

Turn on WP_DEBUG to display your specific error message by adding:

define( ‘WP_DEBUG’, true );

To the top of your wp-config.php file.

Post the error message you see here and we might be able to fix it.