how can restate my Google PR

I am doing seo for a site. its age approximately 2years. before some days it got google pr 3 to 4 . but any keyword is not in listing at that time but. now automatically before some days its pr cameback 0. but all targeted keyword are in search engine top 5.
I want to know how its pr going back and how can i re-improve it.

I have done for it only dir. submisssion
press release subm..
blog comments
forum posting
socail bookmarking
and blog posting only for it.
any reply relative to it will be appreciated.

 

Pagerank doesn't matter.
Position in serps for keyword matters, position in serps for keywords that get searched for really matters.
Traffic matters.
The PageRank that you can see from 3rd party tools like toolbars is an entertainment, a game, a whimsy, an amusement.Don't give it a second thought.

 

Try to build quality links. search high pr websites and use your keywords in your anchor text.

 

according to google.. more quality and relevant keywords can really help..

 

Pagerank is not a ranking factor. Don't mess with it too much. Focus on getting your keywords rank and not on getting your pagerank high.

 

You can do link exchange with relevant sites then get back to PR.

 

I would just write better content, and maybe build some links

 

You can do link exchange with theme based sites then get back to PR....