Planet13 - 5:07 pm on Feb 7, 2012 (gmt 0)

...it used to rank in Google at 7th position for 10 days for the main keyword and for the rest of the 20 days it used to rank at 800th position and this happened for more than a years time, and this was a monthly cycle, so i don't think that it has to do something with the Content or Backlinks...

You are right. It does sound like something other than backlinks or content being the issue. Unfortunately, I don't know what that something else might be though.