97 Dakota spongy pedal and brake light

[eolson04]

I have a 97 Dakota and a couple of days ago the brake pedal started getting spongy, when coming to a stop it would have more than half way of pedal travel and if i took my foot off the pedal and pressed again it was fine until i stopped again. Thos morning the abs and brake warning lights came on and still spongy pedal, with the warning lights on now, if i release the pedal and press again, i have pedal after hearing and feeling a pop and the warning lights go off until i have to stop again. Fluid is full with no signs of leaks, any help would be appreciated.