I run a website <snip> that was receiving around 3000+ hits a day, and now this has fallen to around 500 and i need to find the main reason why?

There are around 400 pages. I have noticed that for some reason the page rankings have dropped dramatically in google results & wondered if it is down to a recent major google algorithm change.
The drop has happened during the month of August & before that, the site has always been high. I have not linked to any bad areas & am not doing anything that i wasn't doing before?

Could you have a look & maybe make some suggestions as to what could be the cause as i have no idea where to start?

Looks like an MFA to me...

Only one thread is needed for topic; the discussion has continued on in this thread, which was started in January on this topic:

http://forums.searchenginewatch.com/showthread.php?t=9512