Germination problems?

I recently got a dark green/black seed from a friend and I placed it in water and put it in a completely dark area to try and germinate it.it has been in the water for about four days and it sunk after the first. But I still don't c a root or anything ofbthat sort to show that it is actually germinating. Is their any hope or anything I can do to help it germinate? Or any signs I can look for to c if it is germinating?

1. You could of put to much water on it.
2. Make sure seed isn't cracked/smashed.
3. When I germinated my seeds not all them sprouted. I suggest you try multiply seeds instead of just one.
5. What kind of water you use? Tap water needs to be sat out for a day or two before using it.