Blog not ranking

I hope someone can help me here. My website has a page rank of 3 and a page rank of 2 for most of my subpages. This is no problem as although the ranking is somewhat low it is still ranking within Google.

The issue lies with the blog section of my website. The main blog page has page rank of 2 but the sub pages have a pagerank of n/a. Some of these pages are over a year old and still have n/a pagerank. I can’t understand why this is as the content is original and when I add pages to the main part of the website they always gain pagerank after a while.

What am I doing wrong?