Almost certainly lack of water!

or conversley too much water that has caused the roots to be 'starved of oxygen'.

LOL I was just looking at one in my S.I.L s house on monday!! she had imitation cosmia stuck in it as it was very limp and she said had never flowered!! it was as DRY as a bone!! and Id like to bet it was starving!!

Lack of light can make it go limp, too. It shouldn't get direct sun, but more than 6 feet from the nearest window is too far.

Peace lilly's (Spatiphyllum walisii) are tropical bog plants and like to be kept moist at all times. Ive even grown them in tropical aquariums totally submerged.

However, they wont like sitting around in water in mid winter when it's cold and dark. This is when rot can set in around the roots.

They are one of the few plants which seem to tolerate dark conditions the best...they just won't flower.

Adjust your watering to suit the seasons and light conditions and it will thrive

I too have had them in shallow aquariums in the past. the flowers need to be out of the water. so they can pollinate.

i dont know but it definatly sounds peaced of lol . sorry couldnt help myself . just add water it will be fine id imagine lol . good luck .

Too much direct light and not enough water

I've grown them in water also, but I have found that they need a very porous, mineral-based soil mix--mainly grit and gravel--to do well. Organic-based soil mixes both stain the water, and use up oxygen, as they decay.