Bon c'est vieux, mais ça arrive encore surement a d'autre, car ça m'est arrivé avec le jeu a jours, voici la solution :
"After Elder McNamara grants you full access of the bunker, heading for his chair, if the player sits in his chair he will stop his action and stand still forever. This can be fixed by going into the console, selecting Elder McNamara with your mouse or typing prid 000e2f87, then disable, then enable.
Note: If you can't find him, type player.moveto 000e2f87 and warp to where he's stuck contemplating a wall/air vent."
(http://fallout.wikia.com/wiki/Nolan_McNamara)