Ranking dropped, Now how to diagnose the problem ?

Do anyone know how to analyse the problem of dropped ranking ?

Please elaborate more on the problems that you are facing.. Ranking dropped from which position and where is it now? What are the methods that you had employed (if you were doing backlinking)

We can certainly help you, but we need to have as much information as we can have to be able to help you out!

If the website concerned is th one in your sig ...then there is one obvious thing I can see..
Your permalink structure is not SEO friendly..Instead of having links that end with #6
You should have links that use your keywords
#6 means nothing to google

Sorry for i didn't provide the detail, I apologise.
I was ranking for certain keywords that are in my signature. All the keywords link back to the Home page. I successfully ranked them up. All my keyword remained on first 5 positions for at least 3 months. I gained good conversion as well. Now last month i dropped my rankings for all of them i waited for a month but couldn't gain the ranking back, all the keywords are now not in the 100th position. I had used associatomatic as my CMS. Last day i deleted it and uploaded the wordpress.
mrgee said #6 is nothing for google, but i gained the ranking upto first 5 positions. It means it #6 didn't have any side effect. I have also ranked other websites by # method. Those havn't lost the positions. I do just profile links for link building. If other sites didn't have any effect of profile links then how can i conclude this is the fault of worse link building strategy.
I thought it would be the associatomatic, that is harming my rankings.
My question was, from where and how to start diagnosing the ranking dropped ?

Thanks!

^ nothing to diagnose, **** happens. If you were getting good conversions, why not invest in some high quality blog posts, maybe a ALN blast or a press release?

Last week my ranking was gone on Google.. I have tried The W3C Markup Validation Service and let my webmaster fix the errors and my ranking were back to page 3.

Without investigation this are some reasons why:

1. competition out rank you.
2. google dance [it happens once in a while, nothing to worry, you will pop back up again, just keep building links]
3. some errors on your site. [your webmaster might have changed something]

this are just general reasons, of cos there are many other reasons upon analysing.

Have there been any major changes to your site?

I think you should first check if some of your backlinks are gone. For instance tumblr links can go down.
From what you say if you built just profile links, there are little chances of all those backlinks to be gone. However I would suggest building backlinks as diverse as possible. Try mixing in some blog comments, directories, press release, article marketing, and you will see your rankings go up again.

links devalued or gone you had built some very low quality links

If you have not done any major changes to the site then consider building some high quality links to your site and you should be just fine.