My main page disappeared from google index again,what can be wrong? i didnt make black seo,or selling links
Try "cache:www.yourwebsite.com" in the Google search bar. This will show if your are in the index. If not then go to webmaster tools and submit your sitemap again to Google. If your website is listed but you have fallen from the ranking then its becasue you website is not deemed relevant to that search keyphrase so bettre SEO is needed.
Try using site:domain.com syntax to see if your other pages are still there. May be your index page is not within the first few results. How did you check that your index page dropped out of the index?