goodroi - 1:41 pm on Oct 13, 2011 (gmt 0)
It would be helpful if you could provide some more details.
What is the toolbar pr of your site? (Not that tbpr is accurate but it can help with diagnosing)
About how many unique domains are linking to you?
Have you checked to see if there have been any changes in your backlinks?
Historically how much daily traffic did you have from this keyword before you started fluxing in & out of the serps?
Have you checked that your hosting is up 100%?
How often is Googlebot crawling your homepage?
Have you used Webmaster Central to fetch your homepage using Googlebot to see your content as Google sees it?
Have you checked for any duplicate content issues?
Have you checked for any malware issues?
How large is the rest of your site?
What is going on with the traffic for the rest of your site?