Non-Muslim leader

Q: Today I was having a debate with a very loving uncle of mine regarding the issue that whether a non Muslim can become a ruler of an Islamic state or not. We didn't end up with any conclusion so I need your help. I'm of the view that a non Muslim can become a ruler provided that he has all the abilities required in a genuine leader and can make the state prosperous. So what does Islam ordains us about this matter. If the answer is "YES", then it's ok for me but if "NO" then kindly answer my following queries:

  1. If he can't become a leader then in my view its injustice with him owing to only this reason that he has born that way which he had no control of?
  2. He lives in that state and loves it and can sacrifice his life for his motherland like any other Muslim can so where's the difference?
  3. In such debates, just to make an argument, we assume any such supposed leader to implement all the things which have been prohibited by Islam on us even though our constitution doesn't allow any such rule to be passed. So even then why is Islam not allowing it?

When are duas accepted?

Q:

  1. Are Duas accepted yes or no - my answer would be 1) Its answered now 2) It may be answered in future 3) You will get it answered in Hereafter. 
  2. What about statements (ahadeeth) ALLAH has forgiven and made you enter jannah and saved you from Hell.  Its like Jesus pbuh dying on cross or something a little like that.