The domain has been active for at least 5 years and had lots of SE traffic until the last few updates by google and until we changed to Vbulletin 5 connect! Now I checked with the tool http://www.rankchecker.com/ and it says Link Popularity is -1!! All traffic has also dropped dramatically after the changed mentioned above! So what to do now?
You need to find out why you've dropped in your ranking. Check your links. Do you have a lot of links from a particular site or type of site and Google's algorithm change has now reduced the importance of those types of links? Your site might have been penalized by Google for having too many low quality spammy links Check you content. Penalties are also given out for low quality content. If you've got poor quality content then start working on that asap! If you've got poor links then start contacting the sites and asking them to delete the link to your site. In the mean time start trying to build some quality relevant links that can help your ranking improve.