Lost SERPs Google Ranking! Need help!

Also I checked for backlinks, all my backlinks are gone! However, when I check site:http://www.mywebsite.com still shows on google. Any one knows why is this happening?

If that site wasn't your big income earner, I would just make new one... Like pople above said, many things could happen and it's really hard, if not impossible, to answer accurately to your question.