While traveling at interstate speeds (about 68 MPH) a vehicle in front of me (about 6 car lengths ahead) hit a pickup truck. I hit the brakes and then my car's auto braking system was activated (displaying on the dashboard) but it did not feel like my car was slowing down. I then proceeded to push the break all the way to the floorboard and my car did not slow down causing me to hit the vehicle in front of me. It felt like the auto-breaking system was preventing me from applying full braking power. When I pushed the break petal to the floor it felt like I was pushing on air. There was no resistance on the petal as there normally would be. There were no skid marks on the road and after the impact, my vehicle would not move. I had to put the car in park and then back into drive to move off the road.