Help. i have all the pieces needed to summon the avatar in suldanessaller and the two stone pieces, but whenever i put the pieces in to summon the avatar in the middle of that room, it does nothing!

i am also have trouble in the cult of the unseeing eye quest. when you have to chose the answers so you can get over a bridge that has fallen down, i accidently chose 'i will come back later' or whatever that option was, and now it wont let me do anything!!!!!