What reasons can make main keywords disappear in search result?

Recently I notice the main keywords on my site are missing, even disappear in search result. But the longtail keywords keep first page. What reasons can lead to this? I changed the layout about two months ago.

 

it's back, at second page.

 

Well, the reason is that longtail keywords are more targeted and more effective. Also they are often niche one.

 

Agree with you, but can't understand why Google kill the main keywords.

 

All that works on the relevancy factors of a page! If Google find a page to be the most relevant to the search term then it displays the same! If your page was there in the first page and decreases to other pages, it means your competitors are doing better than you or your page relevancy value is lesser in Google's view!

 

That's classic sandbox behaviour, your competitive phrases appear then drop & the longtails continue to rank ... build backlinks, content & exposure and wait it out!

Am I in the Sandbox? Here's How to Check

 

When consistency and quality get rid in your work. Then you will get down in search engine.

 

Thanks for your answers, guys. They are very helpful to me.

 

main keywords disappered in search result if you not work while submission.

 

Cuz your competitors fight against your reputation. You need to increase your main keyword anchor link if you want to rank for that main keyword again.

 

How do I know about that? I will try it. Thanks.

 

A lot of webmasters are reporting this..
http://www.seroundtable.com/archives/022128.html
http://www.webmasterworld.com/google/4125460.htm

 

Targeting your main keyword does not always make your site rank higher for that term. Even using different phrases will help. A lot of it has to do with on page factors.

 

I'd like to take a look~~ thanks

 

Agree with you, I will do more tests on it.