Site Dropped to page 3 from page one over past 2 months

Site on a slide, what can i do to reverse the trend

[hughie]

So i have a site that sells 'widgets' it was doing very nicely in lots of search engines but has gone on a bit of a slide recently.

it has a google PR of 5
has plenty of the keyword mentioned in the site
used to be at no.4 in google but since november has been on a bit of a slide culminating in position 19-25 around about now.

What can i do to reverse the trend, it has lots of inbound links although not all are listed in the link:widgets.com (i assume becuase the other links have PR<4)

I have a H1 and a H2 on every page mentioning the keywords (around 10 pages) which all say the same thing, is this going to cost me?

The content on there has been a bit static of late so that is also something that could be upsetting matters.

Any help would be appreciated
cheers,
hughie

[hughie]

I will add actually that the site is doing quite well in Yahoo( first page) but no where near as well in google. Could be some evidence of the shift between the two.