So much work and so many calculations have been brought together at this moment where Mr. House proves to the Mojave that the New Vegas Strip is his, and his alone.
Quick walkthrough
All or Nothing
Enter the offices.
Install the override to allow House to gain control of the dam in the control room.
On the same floor, go southeast past the 2nd Tower exit (with the kitchen) and open the door to Hoover Dam Power Plant 1. It opens to a balcony with the switch that powers the East Power Plant on the western wall.
Go back topside to deal with the Legion and NCR on the eastern side of the dam.
Enter the Legate's camp to deal with Lanius. It is also possible to talk them into leaving the dam, with a Speech challenge (100 Speech) or a Barter challenge (100 Barter).
Return to the camp entrance and deal with General Oliver by either defeating him, or passing a Science, Barter or Speech check of 100.
Reward: Completion of Fallout: New Vegas and the All or Nothing achievement/trophy
Detailed walkthrough
The Courier will spawn at Hoover Dam, where immediately NCR Rangers will be fighting the Great Khans (if the Courier did not make them join them in the quest "Oh My Papa") and Caesar's Legion. The tower that must be entered will be the third one on the right. The Courier will see two NCR heavy troopers who will turn hostile if the override is planted, but they can be lied to with a Speech check of 75, allowing the override to be used without having any of the NCR soldiers turning hostile, which is easier for the escape. Once the Courier has uploaded the override, they should head left until they find the door to the main power plant, where just outside there will be an electrical switch to turn on the power for the Securitron army. The Courier should then head back in, find the key to the exit door and go back to the dam where they'll witness the Securitron army razing all of Fortification Hill to the ground and head east towards the Legate's camp. Securitrons will be helping the Courier fight their way to the camp.
Once at the Legate's camp, the player character must either kill the Legate and all enemies from Caesar's Legion or convince the Legate to retreat with a Speech of 100 or a Barter of 100.
Once they are done with the Legate's camp, the Courier must head back towards the gate where they must deal with General Lee Oliver and the NCR army. They can either kill Oliver and his men or convince him to surrender the dam with a Speech of 100, Science of 100, or a Barter of 100. After dealing with Oliver, Mr. House will roll up in a Securitron Mk II, tell them Oliver and President Kimball's likely fates, and end the quest and game.
Quest stages
Stage
Status
Description
10
Go to the Control Room in Hoover Dam and install the override chip.
20
Activate the eastern power plant to power the Securitron Army.
