Being de-indexed either means that you have misconfigured your website so as to tell Google not to index it, or Google has just decided to de-index it. The first reaction to a de-indexing is to think of it as a Google punishment for suspected black-hatting. However, since Panda, other people have reported webpages disappearing from the Google index for a few days and then re-appearing. This might be your problem.

Google gives more priority to the content of the page.Your home page is not indexing.So, try to change the content of the home page.You also need to change it regularly to get noticed by the Google.It will help to get the indexing back.Also try to get more back links to improve the key word count for better indexing.

Like others have said, try checking your webmaster account ..

Have you been doing any black hat SEO? it might have been deindexed for that, but if you haven't then it's strange, make sure you have a sitemap and attach a high priority to the page and add the sitemap to your webmaster account.. update the page then fire some inbound links at it, maybe with social bookmarking sites so Google spiders find it

submit home page in quality website than after it will be indexed.

it might be the google dance. your home page will be indexed again for sure