Using Hash in C#

I have lots of objects. I should evaluate one of thier members.them one by one. The first is evaluating them one by one --------> pseudo code

while (anyObjectExists)
{
      Class1 obj = getObject();
      double evalNum = eval(obj.member1);
}

but eval is a time consuming method. and lots of objects have same member1. member1 is an array of type sbyte. So I tried to ind another way. That was my way: ------->pseudo code

HashTable evaluatedObject = new HashTable();
while(anyObjectExists)
{
      Class1 obj = getObject();
      if (evaluatedObjects.Contain(obj))
      {
            double evalNum = evaluatedObjects[obj];
      }
      else
      {
            double evalNum = eval(obj.member1);
            evaluatedObjects.Add(obj, evalNum);
      }
}

I knew that I should override getHashCode and Equals method for sbyte. As you can see the eval method only uses member1 from Class1. So I added to methods to my Class1 in this way

    public override int GetHashCode()
    {
        return 1;
    } 
    public override bool Equals(Object compareState)
    {
        if (!this.member1.SequenceEqual(((Class1)compareState).member1))
            return false;
        return true;
    }

Ok. I thought it is done. But when I run my program ... it is a god damn slow program. It is a lot slower than the first program. I tested it. It can find added objects. There is nothing wrong about it. But it is very very slow. I though hash can retrieve data in 1 or 2 shot. What did I wrong?

Any help would be highly welcomed.