1996 GMC sierra brake problem?

I have a 1996 gmc sierra 2 wheel drive pick up. today I was stopped waiting to go, I kind of nudged forward and the brakes just ceased up. and there was a hissing noise like an air leak coming from the brake pedal. then the engine died. I started it back up and continued on with no problem, then a while later it did it again, but this time the engine didn't die put it sputtered like it was about to. does anyone know what this might be?