The Infiltration into Hammer Industries Headquarters was a successful attempt by Black Widow to regain control of the War Machine armor and take down Ivan Vanko.
Tony Stark threw what he believed would be his last birthday party and promptly proceeded to get drunk whilst wearing the Mark IV armor, forcing his friend Lt. Colonel James Rhodes to don the Mark II armor and subdue him.
Rhodes flew off with the Mark II and turned it over to the United States Air Force. General Meade ordered Rhodes and Justin Hammer to weaponize the suit.
Disgraced, Stark was approached by Nick Fury of S.H.I.E.L.D., who provided him with a chest of his father's old artifacts that could hopefully be used to find a cure for his Palladium poisoning.
Reviewing the film reels in the chest, Stark discovered a message from his father that led him to the original 1974 diorama of the Stark Expo: in reality, a disguised diagram for the molecular structure of a new element.
Stark hand-built a Particle Accelerator with the aid of his computer J.A.R.V.I.S. and synthesised this new element, creating a new triangular chest Arc Reactor that cured his poisoning.