What kind of penalty/filter might this be?

[SEOPutte]

I have a site that was ranking very well until about 8 weeks ago when more or less all the traffic disappeared.

Here is the situation:
* Domain showing as nr 1 for the search "mydomain.com"

* link:"mydomain.com" shows no backlinks.
It has alot of backlinks that google has found when i check google webmaster tools.

* site:"mydomain.com" shows all the pages that should be included.

* When searching for my main keyword a directory site:s subpage with my site is ranking as nr 8 and my actual site is ranking as nr 80.

If anyone can help me understand what kind of penalty/filter this might be i would be very grateful!

[tedster]

Could be a lot of things - including a Google bug. Have you done anything that you know is over the line regarding the Google Guidelines?

[SEOPutte]

The site should be fine when it comes to google guidelines. I can also add that most of the subpages rank from position 50-90.
I have had the domain for some years but it has only had real content on it for about 6 months so itīs a quite new website.