If my father passed away but did not leave a Will and now my stepmother will not allow my brother and I to have any of his belongings, what can we do?

I am so sorry for your situation.  If your Father did not leave a Will then he is said to have died "intestate" and the intestacy lawsin the state that he resided in at the time of his death will apply. Now, that statute will distribute his estate that did not pass automatically to his wife at the time of his death.  Anything that was jointly held is not part of his estate.  When you say his belongings do you mean his personal effects?  Is there any way to appeal to her through a close family friend or relative? You have both lost someone you loved and it is hard to part with things so close to their death.  Maybe time will help.  Otherwise, seek legal counsel in your area.  Good luck.