I've gotten all the pieces but still can't get to the top. I followed the advice in the other post but to no avail. Please help me, I'm going nuts here.

when you find the room with all the seperate stairs leading up (the large room with all the non-hostile shades), take the stairs along the right edge of the screen. (I may be wrong about which stairs it is, but I know it's from that room.) You'll go to a room with a dirt ramp... take that up, and keep going up until you find the room with the astrolabe. Good luck.