It is very simple. The number of your competitors growing day after day. The better optimized sites come with the more relevant keywords and the more backlinks than your site.

mcnellie wrote:

my site has been number 1 on google.com for the key words "tikal hotels" for 7 years. We just moved the server to a secure option for credit cards and this required an IP address change. We are now not in the top 100 pages or more. Any ideas of how to get back to number one.

http://www.lacasadedondavid.com

Bruce McNellie
webmaster for lacasadedodavid.com

Dear Bruce, thank you for your question.
Your site isn't indexed at google and yahoo any more. Here is what you can do to get it re-indexed.
Google:
1. Go to http://www.google.com/intl/en/submit_content.html

and choose "Google Webmaster Tools"

2. Create a google account and add your site and site feeds like google sitemap and robots.txt.

You will find the best sitemap genarator at http://gsitecrawler.com/

You can add multiple sites and track them. They should be indexed within 3-4 days.

Yahoo:

1. Go to http://siteexplorer.search.yahoo.com/
However, to add and track your site you will need a yahoo account if you don't have it yet.

2. Add site feeds.

In both cases you will have to verify that you are a real site owner by uploading google and yahoo verification files to the directory where you host your files.

Best of luck