Brake problems

I have a 1995 oldsmobile lss non-supercharged, and I was pulling from a driveway when suddenly the vehical started to loose power and the front brakes completly locked up. I shut it off and turned the vehical back on and the brakes released. I then proceed to drive and about 2 minutes later the vehical did the same exact thing but this time all four brakes locked up. Does anyone know why it would do that?

Welcome to AF. Bad master cylinder, contaminated brake fluid swelled the pistons in the M/C, power brake booster also.