Question about SERP keep dropping

All right then, I finally have a little knowledge on IM after some months reading. And Im able to rank simple EMD websites. Mostly just bookmarking and submit to ALN and their fine.

But I have a slight problem, I have still one very important website I invested over 5k.

I started of buying(hiring) a strong PR7 some months ago (Which dropped to 6) anyway Im talking about strong and paying around 100$ a month for it. A website with a REAL PR7 and 50k visitors daily.

Slowly I have gotten to place #4 for my keyword.

Now the bad(I think now) part I have hired a SEO guy on a freelancer website wich got me around 800 backlinks(I can see in webmaster tools), mainly directory, forums links and such. Because I didnt know what to do else back then.

At the same time I hired another real PR7 For wich, still is, for a price of 150$ monthly. No bs crap here, real quality PR7 again.

The only thing that happened in the last few months is dropping and dropping.

I have no notice from Google in my webmaster account, but my site is now ranked #18.

While with my knowledge, it makes no sense at all, all websites above me have little no backlinks or not even related to the subject. (mine is PR5 now)

I got the one PR7 also to another website linked and that website is ranked #3 for the keyword, without any other linking. So I think its not that PR7 site because its a real authority website also.

Anyone knows what I did wrong here? Or any suggestions how to fix this?