I just started a new game, and reached Riverwood. Suddenly, no one's moving. everyone's standing in the exact same place, and not following their schedule. Even Halvar's just standing at the entrance to town. The girl who's supposed to lead me to the Barrow walks outside and then stops. Its like the exterior AI no longer exists. Um, help?

My AI pathing is all sorts of screwed up on my new savefile, as well. Couldn't start the main quest, had to restart... Carlotta wouldn't lead me to the bridge (and with dragons eventually showing up, I didn't want her stuck outside). Most recently, I walked into Jorrvaskr for the first time today, and the fistfight not only migrated to the other end of the hall, but wouldn't stop. Njada and Athis just perpetually beat on each other.

stop/uninstall all mods?

Found it, it was a Riverhome house mod I got off Steam Workship. It screws up pathing in Riverhome. Deleted it, life is good again. Reloaded the save, and suddenly everyone walks like nothing was wrong.