Authority site with low PR?

HI, I run a non-profit Budddhism site, which is considered as an authority in Buddhism. The name of the site is e-Sangha.
The site is listed at Yahoo! at Religion section .
This site is also listed at DMOZ at the Buddhism Chat.
We have an alexa ranking of 60,000 and according to Alexa, we're the most visited site on Buddhism. You can view the details here.
Hundreds of sites link to us, the higher PR ones include open-site.org, buddhism temples, buddhist magazines, countless blogs etc.
Our main page has a PR of 2 and you can see the details here.
Our famous forum recently had dropped from PR4 to PR1 and you can see the details here.
Our internal pages inside the forum also has a PR1 or PR2.
Frankly I do not know what is going on. Can anyone please advise what should be done to improve the PR?
Thanks.

Hi teyes,

WHen I look at the toolbar your main page has PR 4, my eyes also tell me that your forums is PR4 also.

your site is probably new. I saw only 14 backlinks to the site on Google.

The PR fluctuate between 4 and 2, and my front page has a PR2 which was dropped from PR5 one month ago. It also begin like fluctuating and then suddenly drop.
Pages with high PR linking to us include
Lama Yeshe Wisdom
Open Site
Tibetan Liberation Organization
and hundreds of blogs that point a link to us.
I was very much worried that our PR for our forum is going to drop just like our front page, as its again showing signs that something is going on.
The funny thing is that somehow, probably we did something wrong that we ourself do not know, we're not listed for keywords like Buddhism, Buddhist etc. We get most of our traffic from Yahoo! and word of month, and through all these links form blogs, websites etc.

Exactly, probably this might be one of the problem. Although if you search link:www.lioncity.net/buddhism you see only 10+ backlinks, if you type e-sangha, you can actually see thousands of different websites pointing to us.
Besides Yahoo! and DMOZ and the few sites listed above, other sites that link to us include
http://www.cafeshops.com/esangha
http://www.academyhd.org/blogarchives/000145.html
http://www.dhamma.ru/sadhu/modules/...?cid=42&lid=106
http://cosmiccharlie.blogspot.com/2...ie_archive.html
http://www.newsisfree.com/sources/info/11509/
http://www.tipitaka.net/links/
and all these are not relected when you check backlinks and my site is not really new, we became a Buddhism forum June 2003.

You're PR4, you probably forgot to check it with www. infront of the domain name.