"I just add Freebies4webmasters banners but I added in other websites too and the PR is the same" If you have added any paid links without nofollow tag, then that can hurt your PR. And it is very much possible to not get penalize on all the sites. That is, if you have paid links on your other sites too, and if they still have their PR, then it is because google hasn't so far found about the paid links in that site. I suggest you add no follow tag to any paid link in your site and then request for a re-inclusion in google webmaster tools.
Yeah i have the same problem too. PR 3drop to 0 and pr 4 drop 2, but notraffic change. I still get huge traffic from google, anyone kown what's really Google doing ?
Some people say that Google is not realy taking away the PR. They just delete it from the toolbar. I do not know if it is true. But it would explain why you still rank in the SERPs.