You should check if the IP on which your website has been blacklisted by the SE. If you are hosted on a shared server, there is a single IP that is shared by all the accounts hosted on the physical server. If any of the account/s are involved in spamming, other websites too have to pay the price. It is always suggested to have a dedicated IP assigned to a domain to avoid such situations. You must try to add fresh content to the website, and after a week of two check if the content is getting indexed in the SERP.
Though this is just a possibility. There might be multiple reasons for such a change. One of those is as mentioned by ldcdc. You must get your website reviewed from an SEO expert.