oops. I hate when that happens
, the powersteering and power side of the GM powerboost brake system are designed to use power steering fluid(hydraulic oil with lo temp addatives, ATF is a common substitute that has comparable properties and addatives to provide the lubrication requirements or the hydraulic pump and be compatable with the internal seals in that system.
Brake fluid has different properties to handle the high temps associated with brake use, it is thinner and does not have the lubricating properties required for use in a pump, it also is usually not compatable with the seals in a hydraulic system. I know it's confusing but hydraulic brakes and hydraulic systems(power steering) are 2 seperate animals even though one is used to operate the other. Anyhow drain and flush the steering system with ps fluid or ATF and see what happens, hopefully the steering pump and related seals will resume operating, if not check the pump output pressure & flow or install a fresh pump and check for operation.
if you need more info pm me