You will start in the location with lots of red snakes. As you know, Indy is afraid of snakes and will escape from them. You must find a way to cross the gap. Use you whip on the highlighted place. You will notice small bridge to pop-up.
Change your character to Sallah, jump above the gap and push forward two monuments on the left and right side of the gate. Build a pile of wood from LEGO pieces and set them on fire using torch. The bridge will fall down and will startle the snakes. Take the blue book from the middle of the room and stand on the white button near the gate. Wait for the second character to stand on the second button - the gate will open.
Watch out for the orange buttons - try to avoid them. Kill all snakes with Sallah. Use blue book near the hieroglyphs. You will notice, that four of the pictures will shine. You have to "click" them in the same order to open the door.
You will be in a big room. When you try to go up stairs, the stairs will change into glossy surface and you will fall down. Kill little bugs. Take the key and use it on a mechanism on the right side of the room. Destroy the wall behind the door. Kill the bugs and make a monument head from the LEGO pieces.
Take it and put it on the place with white arrow. The stairs will appear but don't use them yet. Take the orange LEGO piece and attach it to the pillar near the mechanism.
In the room you will notice four this kind of pillars. You can turn them. Push the pillar which is shown on the screen above, so the foot-bridges will be close to each other. As Indy, use the rope to climb on the pillar and jump to second one. Change your character to Sallah and turn the pillar with Indy, so the foot-bridge will point to the right side. Now, turn the pillar on the right, so its foot-bridge will be pointing to the left. Change you character back to Indy and use whip to jump to the pillar on the right side of the room. As Sallah, push the pillar with Indy. As Indy, jump to the pillar with the diamond and take it.
Go upstairs and step on the brown lift on the left side. Put the diamond in an eye of the statue. Get down, take the brown LEGO piece and put it on the green pad. Take the diamond to the left, and step on the lift to the right. Put the diamond in second eye of the statue. The way is clear.
Destroy the wall to the left, take the LEGO piece and put it under the middle hole in the wall. Take the golden ball from the floor and put it in the left hole. As Sallah, dig up next ball, and put it in the middle hole (use the lift, which you have just made using the LEGO piece).