Go to your EIG/Hostmonster control panel and find the Apache/PHP error logs. If you can’t find them, contact EIG/Hostmonster support and ask where they are located.
By any chance did you edit a PHP file in a plugin or theme just prior to this problem? If so, that’s the file you will need to restore to its original state. If it’s a plugin file, renaming the plugin directory will deactivate the plugin, and you will then be able to get back into your site.
Otherwise, if the problem is a code error, you will need to fix it yourself. If it is a server error, contact EIG/Hostmonster support again and request that they fix your site.