Skyrim Dawnguard Bug, Help Please!!

So I just got the Dawnguard DLC for Skyrim. I'm playing through, and after I become the vampire lord and go through the tutorial with Serana's father (forget his name), he tells me to speak to the other guy for a quest. As soon as I walk out of the doors of the chamber, everyone in the castle attacks me. WTF is up with that? In addition to that, I've continually screwed up, causing my to have to restart the questline 5 times. I'm tired of having to do it over and over and over again, and if this bug occurs one more time, I'm going to throw my computer through a window. How to do stop it from happening? Do I need to make a new character and start over (not that big of a deal thanks to console commands)? Do I need to reinstall Dawnguard?  Please help me!!!

Try downloading the Unofficial Dawnguard Patch on the Workshop or Nexus. You may have to restart the quest though.

Try downloading the Unofficial Dawnguard Patch on the Workshop or Nexus. You may have to restart the quest though.

INF1DEL

Have you downloaded new mods just before or after Dawnguard? I had some mods that conflicted with my character save, I kept crashsing when I entered Breezehome, only way to fix it was to make a totally new character. Guess the old save has issues with certain mods.