Time for some investigation by: Jacki Cammidge, Certified Horticulturist
It looks like it's time for some investigation. I am interested to know what exactly is going on underneath the surface. Is it possible that the 'plant' is actually just a bunch of cuttings stuck in a pot? If so, this is not really going to be successful. You didn't say how long you've had the plant, or where it came from, so there's no way to know the background.
What I would do is to carefully remove everything from the pot, and see if there are actually roots on the 'stems'. The one that is withered is most likely a goner, and not ever going to be brought back to life, but the others might make it.
ZZ plant, or Zamioculcas zamiifolia (you can see why it got shortened!) need bright indirect light, and overwatering will definitely be its downfall. Yellow leaves are typically the main symptom. Due to the fact that this plant has rhizomes under the soil, these will rot quickly with too much moisture around them for long periods of time. Regular potting soil with added lava rock, pumice or pea gravel will give it the drainage it needs.