I have about 300 hours in the game and am pushing Level 70. Quite awhile ago, I was at the Cabot House seeing if Jack Cabot would let me in. I was traveling with Ada the robot at the time. All of a sudden she is attacked by Rust Devils and we killed them off. Now I am unable to do this quest. I am told the door is open and there is a ghoul in the living room who won't talk to me. Any way to trigger it??

I haven't had that particular problem, but you could try opening the console and clicking on the ghoul and type disable.
After he disappears type enable and close the console. See if he talks to you then.
I have used this method on a couple of NPC's to advance a quest.

Well, I guess the 10th time is the charm?! I went in to try what you suggested with the console, and there was Jack Cabot ready to talk to me!

Thanks for the suggestion and I'll keep it in mind!