[donut]

Crawl underneath and start looking.
Sounds to me like you lost hydraulic pressure (soft pedal, warning light.), Could be a pinhole in a steel line, wheel cylinder, caliper seal, rubber line, or even a seal in the master, though I'm not sure if the master will pop the light, don't remember.

IMO, start checking one end to the other. If you can't find it. have someone hold the brakes and look again.