Hi ammuth,
to the site!
Does the container have drainage holes in the bottom? Peace Lilies require bright indirect light (never direct sun) and although in their native habitat they actually grow in streams and rivers, when they are grown as a container plant they will require a pot with drainage holes and a light airy soil that is kept consistently damp throughout, not overly wet. A dense soil will retain a lot of moisture and deter proper aeration at root level, causing the roots to suffocate.
I'm sure others will be along shortly to offer advice but meanwhile, here's our database page where you will find pertinent information for this plant and lots of member photos:
Peace Lily (Spathiphyllum wallisii)