You will finally be able to proceed with the main puzzle. As I've mentioned before, it's not too complicated. It will require, however, doing certain things. Here's what has to be done:
1) Head on to the left platform. You will have to stand on it. The platform must touch the floor.
2) Use the grapple and start pulling the smallest crate towards Lara. The crate must be placed on the left platform.
3) Leave this platform (the crate must stay on it!) and head on to the right one.
4) Make a jump in order to reach the right platform. Once you're there, start pulling one of the big crates (#2). The crate must be placed on the right platform.
5) Leave the platform. Stand in front of the statue and make a single jump in order to reach the roof of a small building.
6) Use the grapple to pull the smallest crate. You shouldn't have any problems with that because the left platform will be at the top (#2). Leave the smallest crate on top of the building.
7) Head on to the empty left platform (Lara will have to be standing on it). Let it touch the floor again.
8) Use the grapple to pull the largest crate here (you haven't touched it before). This crate must be placed on the left platform.
9) Go back up and start kicking the smallest box. It will have to join the large crate on the right platform (#3).
10) The left platform has moved to the top. Thanks to that, you will be able to pull the largest crate here (#4). The crate must be placed on the central button.
If you've done everything correctly, you will be rewarded with a short cut-scene. You should also listen to a short dialog. Leave the roof of the building. The main entrance is now opened (#1). Enter the main tomb. The door will close behind Lara, however you don't have to be worried about that. Make a few steps forward. A longer cut-scene should appear on your screen (#2). Lara will finally complete the whole artifact. As a result, she will receive a famous Excalibur blade!
You might want to consider testing a newly acquired weapon (#1). You should know that you will have to use it very soon, so it would be best to practice some of the new moves. Start moving forward. Head on to a nearby door. You have to smash it with your blade (#2).
A new cut-scene should appear on your screen in just a few seconds (#1). The temple is going to be destroyed very shortly. You will have to make a run for it. You should be able to regain a full control over Lara's movements. Start running towards the left platform (#2). Make a single jump towards it. Bear in mind that ALL jumps MUST BE very precise. Furthermore, you won't be able to stop along the way, because there isn't any time for that.
Proceed with the next jumps (#1). Like I've said before, you won't be able to make any mistakes here. Furthermore, you will only have 2-3 seconds to make a successful jump. The last one is by far the most difficult one. You will have to reach a narrow ledge (#2).
Once you're there, a new cut-scene will appear on the screen (#1). Lara decides to revisit a temple located in Bolivia.