After completing the first mission the scene cuts out and goes back to the intro scene asking me to “press start”. When I do I have to re-start the first mission from my last save. I am unable to get to the next mission.
Sounds like a disc issue. Have you tried another Halo 4 disc in your Xbox, or your Halo 4 disc in another Xbox?
Also try installing the game to your HDD and see what happens.