Iv'e been able to get all three satutes, but am unable to open the tomb just by clicking on it, is there something else that I have to do before I am able to open it?

You know there's a search function?

Heck, a few topics beneath yours is a solved question on the same, gruddamned problem

http://www.gog.com/en/forum/inquisitor/tomb_of_st_orthenius_act_3_spoiler/page1

Anyway: Go ro level 2 of hte dungeons beneath the archiepiscopal palace, find a talkable bookshelf in s-w corner. That's it.