Athenasmiles

I have played through the entire game and now I am in sun in shadows and cannot get down the staircase to where I believe Thaos is waiting. The interact button simply will not pop up. I have tried restarting my game, reloading, leaving the map and coming back. I simply am stuck right at the top of the stairs. I would very much like to actually finish this game which I have spent so much time on. What can I do? I am playing on a PC.