Looks like all your roots rotted. Plant might be beyond saving if that's the case. My mom has a ten year old peace lily and she neglects the crap out of it. For the most part, they need watered once a week in summer to maintain evenly moist, but not wet, soil. Cut back in the winter, about every 10 days to biweekly. That's just my experience. You may have been overwatering or the pot could've been too large.
