If your grandfather himself didn't become a citizen, your grandfather can't transmit citizenship to any of his children or other descendants.
It's possible your grandfather became a citizen at birth, but even if that is true, one of your parents (the child of your grandfather) must have been a citizen either before you were born or before you turned 18, in order to pass on citizenship to you. I see you haven't mentioned anything about your parents.
EB3 ROW I-485 Approved: July 2007
USC: July 2013
I am a layman, not a lawyer. What I write here is not official or professional legal advice. In addition, my answers on this forum are specific to the scenarios discussed in each thread and should not be generalized to other situations.