Welcome to new site hell. Happens to most new sites. Shows in the ranks for a few days/weeks, then gone to ranking neverland. Just keep pluggin, grow your links, add fresh content and give Google a reason to rank you high.
I think patience is the real solution for now...mostly it takes some time to show results.....Anycase I think you should better try to check out the following....Look for some natural cause. I mean 1. See if someone has changed the robots.txt file and inadvertently stopped the search engine spiders from entering your site. 2.May be your web server has too much downtime, that might also hurt. Narender Pal Singh