2004 Infiniti G35 power steering

Your description of the problem and symptoms isn't very clear, but if you're losing power steering assist only in one direction at times or only when the engine is cold, that is typically due to internal leakage in the rack and pinion steering gear. A constant loss of assist always in both directions is usually due to weak power steering pump. If the assist comes back when you raise engine speed a little, that is another clue the pump is weak.