Why did ARCHIMEDES not activate?

Solution 1:

Just making sure, but according to the wiki, I quote:

The terminal on the mainframe contains some notes the player has probably already seen on previous terminals in the building, and an option Configure Power Grid. Selecting it reveals 5 options:

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5 Full region (emergency output level): This solution overloads the plant, which prevents Archimedes I from being activated (see further notes). This gains no reputation with any faction, but Ignacio Rivas will still give the player some rewards.

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If the player has chosen to activate the Archimedes I defense system, and has chosen option 5 (overload) for the power grid, horns will blare and a warning will play about the imminent weapon test, but shortly thereafter everything grinds to a halt. If the player is trusted by Ignacio Rivas, they can now go talk to him to receive awards. Otherwise the quest ends.

You did not do this, right?

Edit: Further down that page:

Bugs

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• pc The Archimedes I sequence may not play out even though activated at the mainframe.

You could have run into that.