There are several reasons why Google would deindex your site. These are discussed below along with remedial action. Getting your entire site deindexed can be very harrowing, although it is only for certain breaches that Google will deindex your entire domain rather than specific non-conforming pages.
Meta Tags - Make sure that the page(s) that's not getting indexed doesn't have these meta tags in the source code: <META NAME="ROBOTS" CONTENT="NOINDEX, NOFOLLOW">
Robots.txt - This text file which sits in the root of your website's folder communicates a certain number of guidelines to search engine crawlers. For instance, if your robots.txt file has this line in it; User-agent: * Disallow: / it's basically telling every crawler on the web to take a hike and not index ANY of your site's content.
@bangthetableDec 09.2016 — #*Check your domain htaccess file. If any custom code were generated automatically, it would stop spider to crawl you home page.
*Just delete your current htaccess file and generate & upload new one. then submit your XML sitemap file and fetch as your home page in webmaster account.