Yay another gamebreaker! This time a quest bug..

I started the Thieves Guild questline. Seemed to be going fine until the end of Taking Care of Business.

The journal updates as quest completed, and you are supposed to follow Brynjolf to get the next quest Loud and Clear. I follow him, he gets stuck next to a cart in the Cistern but I bump it out of the way and he carries on to Riften Marketplace where he just idles. I can't talk to him, all he says is "hmm". I can't talk to Mercer Frey or Vex, they don't initiate dialogue. I can't use the console to trigger the quest, nothing happens when I use the setstage command. I've also tried triggering the quest after Loud and Clear, and using the console to make myself a member of the Guild, but nothing seems to be working.

I've searched some answers, other people have had the same problem but it seemed to be mod-related a lot of the time, but I have no mods installed.
Currently just the main esm (no dawnguard).

Any ideas or should I just give up on the Thieves Guild? :/