This is actually the first site I made using Amazon as the monetization and for the past 2 months it had been bringing sales here and there. Nothing to write home about but it was adding up as it moved up the SERPs.
My site had 4 pages at the top of page 2 on Google and 1 (an inner page) sitting at #8 on page 1. This latter one was responsible for most of my traffic bringing roughly 10-15 visits a day by itself.
I quickly typed the keywords I knew I was ranking for and my site was nowhere in sight. I was like ! Have I been "G Slapped?!"
I did a "site:mydomain .com" and NO results! Now I was really pissed thinking I had been removed from the index. I mean, I've been doing everything above board for my sites. My first thought was "GRRR Darn Google!!"
But then I remembered that I had changed the theme for my site to see if it improved conversions. What I didn't do when I changed the theme, was add the code from Webmaster Tools into the header of this newer theme. So after a few days without this code anywhere on my site, Webmaster Tools was unable to download my sitemap.
I went to the Webmaster's Tools site and indeed, there was a notice for an error with the sitemap. I quickly re-added the code to the theme and the sitemap was successfully verified again.
I will add a new post to the site to see if it indexes again.
From now on though, I will simply use the option to upload the html file provided by Webmaster Tools onto my website. This ensures that nothing like this will happen again.
My question to more experience people here: could this be the reason my site has NO pages indexed anymore? The site had 7 pages indexed before this mishap.