Wait, so you had 4...now you're only down to one? If I remember correctly, aren't you the one who purchased them just a few days ago?
What are your tank params (ammonia, nitrite, nitrate, pH)?
How did you cycle?
What is the temperature?
Are they eating?
Have you done your research? (I don't want this to sound rude, but people have researched dwarves for months and years before even attempting them, have you done yours?)
Is/Are the horse(s) changing colors?
What do you mean they seem fine...if they're dead?
Sorry for all the questions, but by answering them you can really help me help you.