Sounds like you accidentally reset the brake sensor. You're screwed and need a new one now. Or you can un-clip it from the caliper, cut the end off, strip back the wires and tie them together. That will make the car think there is a new sensor and make the light go away.
If you get a new one and your brakes are pretty worn already, the sensor will get crushed and break due to excess travel. They are designed to gradually wear down as the pads wear down.
I think another option is to buy a new one, plug it in, reset to get the car programmed for that sensor, then hook your old one back up and reset again. I don't believe the car will remember the old one after you reset with a new one. And you'll have a new sensor waiting for your next brake job.