Please post a photo if you can. Leaves and roots if possible. A link to it is fine. :)

Take a look at the roots. If they are bunched up pretty close together, I would split the plant in half, replace the soil one more time (make sure it is loose and fast draining), soak in a sink for fifteen minutes, fertilize, and see what happens. Either put the other half in a new pot or discard. Depending on the color of the leaves, it could also be getting too much water. Any mushiness in the roots? They prefer to be watered just as the leaves start to droop. That promotes new flowers. Always cut off flowers that are fading. They like clean leaves. Check for spider mites or other issues beneath the leaves. They aren't very susceptible, but it won't hurt to check. A photo would really help. Check how pliable the leaves are. If they are tan and mushy, too much water. If they are yellow and crispy, not enough. Those are the main issues I can think of at the moment. :)

These plants are suseptible to insects like the fungus gnat; which feed on their roots during their grub stage, the spider mite, and the scale. We are battling with the fungas gnat in our office. You will see them flying around. They look like fruit flys. There are some natural ways to deal with them but we haven't found them to be 100% effective. Cinnamon sprinkled on the soil and apple cider vinegar in little containers to trap the adult gnats. I have also seen where people suggested fly paper. Anyway, if your plant is still alive, here is a link on caring for a peace lily... Good luck.

Here is a link that might be useful: Peace lily care