A few things have been posted about this topic here before. If you search the knowledge community for "Google", you should find what you need to know, e.g. under:

http://tinyurl.com/386qze


Here a few key points in a nutshell again:

1.) Indexing in search engines can take its time. You might be able to speed up the process and positively influence your site's ranking by manually submitting the URL to search engines and web directories.

2.) Search engines can change their indexing and ranking strategy occasionally, thus affecting the ranking of your page.

3.) Indexing and ranking of websites also depends on external factors, e.g. the number of sites linking back to your site and their ranking status.

I hope this information helps.