Page Rank really isn't relevant it was just something Larry Page came up with when they got Google started
The tool bar being referred to is a firefox plug in that you can use with Firefox that lets you see what page rank any site your looking at has. it also provides additional information to use for SEO purposes inbound links etc
What I often see is poor site structure missing basic seo 101 that's really where you need to go check first. Verify your HTML on
http://www.w3.org/
Also make sure you're reviewing your analytics data for keywords that drive conversions it's better to target lower traffic than high traffic low conversion keywords. Sure it's great to rank #1 for sex but the conversion rate would be extremely low