After link building your website may receive low rank or disappear from the index. But your site will again appear and receive high ranking within few weeks. I have seen this for many sites.
May be your site penalized by google or may be its possible that your site go to google sand box. Search about google new algorithm update and try to change your site content again.
Give it some time it might appear. If you have not added new content for a while don't be surprised if this happens, as other sites that have updated content supercede your site
Usually that is the case for newly set up websites. Sometimes a drop in ranking for a keyword means an increase on the other keyword.
From my experience, its common for a site will not appear in the serps for a few weeks to a month when it is being evaluated by google. The key is to stay calm & continue your link building, trust me, it will show up after some time & almost always in a higher position. Cheers = )