Why did the steering & brakes fail on starting?

What is your question?

On starting 2500 duramax 4x4, noticed loss of power steering & brakes. Ist time, when I opened power steeering fluid cap, some fluid spurted out. Put cap back, restarted engine, problem rectified. It has happened again, this time no fluid spurting out, but revved engine & problem rectified. Any advice as to why this is happening & what needs to be fixed/replaced?