general problems of the 1999 GMC Jimmy

I replaced my front pads and rotors. Been fine for a week till yesterday I stopped at a light brakes felt slightly spongey, not long after maybe ten minutes three cars ahead of me had stoped as I hit the brake my foot went straight to the floor and I smacked the vehicle in front of me doing appx. 35-40 mph. It was a four car pileup I took heavy front end damage more or less totaled the vehicle but the airbags had failed to deploy causing me to hit my head on the steering wheel and suffering a concusion. The seatbelt didnt lock as it should have either therefore causing my whiplash to be severe.