I have been making a new save every time I save, so I can go back and start over if I make a mistake etc, and I decided to start over cos I cheated and the game got boring with my character being able to one or two shot pretty much anything below dragons, even on master difficulty. I had also already completed the thieves guid quests so I assume the bug I'm getting isn't because of a save game.

I went to Riverwood, did the stuff there to get the quest to go to Whiterun, but skipped town and went to riften instead. I spoke to Brynolf, did "Doing Business" or whatever it's called, then got the quest "Loud and Clear". I listened to all the dialogue, went to go and speak to Vex for the optional point and I got no dialogue options with her, she just told me to go and speak to Brynjolf. I went to Tonilia, thinking I needed to get the guild armour first, I have no option to ask for it, she acts like I need to speak to Brynolf still, I went and spoke to Delvin, and he gives me an option to ask about the quest or to train me in sneaking. I went and did the quest anyway, and when I got back they were still acting the same way, like I needed to talk to Brynolf still.

Rather annoyed, I started over and spent yesterday doing every quest in Riften and most in Whiterun, I went to the Thieves Guild just now, and I have the exact same problem as I did yesterday.

If it makes a difference (though I don't see why it would), I have wiped out the dark brotherhood and still haven't spoken to the Jarl of Whiterun.

I had the exact same thing happen about 5 quests down the line. Luckily(?) I had to restart my character anyway, because I lost the save. Here's hoping it doesn't happen again....

some times if you delete the Skyrim.ini in the C/....../Documents/My game directory most of the bugs would be vanished. I have got the same problem with the blade boss in ratway at the very first of the main quest.

I tried deleting the skyrim.ini file and the bug is still there, and I don't really want to have to start all over again when I've done that twice in the last day...

It's sad, google it, maybe you can find something.

I tried, I couldn't find any mention of this bug, much less a way to fix it...

I know it's been a while, but I've found the reason for this problem I was having.

After deleting and unsubbing from every mod, uninstalling Skyrim and then completely deleting the Skyrim folder along with my saves etc, I reinstalled Skyrim and carefully checked the comments for each mod I had installed.

The culprit is the "Vendors have more money" mod from Skyrim Nexus (the one that adds 25k gold to every vendor), it completely breaks the Thieves Guild and the only fix is to remove the mod and load up a save from before you started using it. So, yeah, I've learnt my lesson, be careful what mods you grab (though if anybody knows a money mod for vendors on the steam workshop that isn't borked I'd like to know, constantly having to skip two days when selling a huge amount of valuable items is rather annoying).