i can just about guarantee from your description that one or both of your front rotors are bent, badly. when you roll the bike, the bent rotor forces the pistons back into thier bores, and that rubbing makes it hard to push. after they're shoved way back into the caliper, you have to pump the brakes a few times to push the pistons back out before they'll contact the rotor. that's why it feels like you have no front brakes "sometimes". if you ride it like that, it'll probably put you on your ass with a quickness.

get the front wheel in the air and spin the front wheel. you'll be able to see how bent your rotor(s) probably are.