What's up with my disc brakes? (pads replaced)?

I have Avid BB5 brakes on my Gary Fisher Marlin. Brakes were having trouble stopping the bike quickly. Thought that they needed new pads so I just installed them but the brakes still are having problems. I have to squeeze the brake handle all the way to the grip to get them to work at all. Back brakes especially. Help!(?) I'm in a race tomorrow.