So I completed the Civil War questline I killed General Tullius and when I talk to Ulric he says there's nothing to do but I started the Dark Brotherhood questline and I'm on The Silence Has Been Broken quest I've talked to Delvin and have the letter of credit to give to Astrid and she won't talk to me all she says is I've undermined their plans I'm the reason for the seige on Soluitde and not to talk to her until I've fix the mess. I am at a complete loss at what to do!

Cos later on you kill the emperor I think it might not let you I would search it up on UESP.