I would like to know what are the steps needed to check why a keyword is not ranked anymore?
I'm having this problem recently with Google and Bing (since a few months). My website is still being crawled and I'm still appearing Google (& Bing) for other keywords but my bread and butter keyword is now dead for me.
Basically, It's my Home Page that is not ranking anymore with that keyword, other pages are ranked but they are in the 25 to 50's.
Google personalizes search results. That means when you and I search for widgets it is we can see different websites ranking in the top ten spots. These personalized serps make it harder to track keyword rankings.
It is even possible your site is ranking #1 when I search for the keyword but it shows up #20 when you search it. Dramatic differences like that are a bit unusual.
Let's assume your keyword is actually ranking lower and traffic to your site has dropped. This could have been caused by over 100 different factors that influence the algo. Here are some things to look at
Changes to your on page content -Changed the keyword mixture on your page -Your unique content was duplicated on other sites -Over optimized content tags -Site has been hacked & hidden text was added
Changes to your backlinks -Lost links from quality sites -Gained links from spammy sites -Bought paid links from a poisoned network
Changes to your competition -They improved their backlinks -They improved their on page content -They improved their social presence
This is just the start of analyzing a change in SEO performance. Good luck!