Somebody can help me? I have already give the holy water to Kerah and found the earth of Lich...I found one champion's key but I can't open the gate with it...do I need another key and where to get it??

You do need two champion's keys, which are held by two named demons. Both of them are in the smaller pyramid area where you find the Lich's heart, but on different pathways. One of them you get to by going through a room filled with demon temptresses; the other is inside a large room with a pit that eventually leads to the lifts that take you to where the Lich's Heart is. Both of them hold Champion's Keys. When you kill them, they drop the key.

-Sazerac