I wouldn't worry about it too much.. Page rank (PR) is only one of many of the variables used to decide your SERP results Why don't you concentrate on traffic instead... I've never really cared what my PR is, it's just a value, quality traffic really counts
Don't get too concerned about it. PR drop won't affect your ranking. Traffic and SERP are far more important. If these things remain stable, there's nothing to worry about.
As long as your website sell something, PR is nothing. Don't worry. But just for some tips, you should recall whether you haven't updated your site for a long time, so that google slap your site.
Update your site regularly, creating an interesting article, spell check your content and publish articles on other sites relevant to your expertise
Build more backlinks from reputable websites. Upload some unique articles from high PR websites and it will climb back up along with a nice traffic boost.
get some new pr backlinks some existing backlinks may have been removed or the pages carrying those have lost their pr, thus drop in pr for your site
their may be several reasons which result in decrease in page rank like dublicacy,submission in irrelavent categories and more.
I think page rank is as important as traffic itself but you should not worry about it because google performance google dance in which you see some fluctuations in page rank, this phenominon is called google dance, so dont worry about it. and do your efforts.