Spiders look for the robots.txt file in your web site home directory to tell them what they can index.
Have you checked your site robots.txt file, is it allowing the spiders in or blocking them?
The file is a text file with a simple structure such as: -
User-agent: *
Disallow: /wp-admin/
Disallow: /wp-content/
Disallow: /wp-images/
Disallow: /wp-includes/
This file allows in all the spiders but prevents them from visiting the named sub-directories.
Why don’t you do a search in Google for Robots.txt Validator to find the many online services which will report the content of your robots.txt file and let the search engines into your site.