I have encountered a nasty bug where no merchant trade windows will open. I ask "what do you have for sale", and the merchant replies "take a look", the dialogue window flickers, and no trade window appears. This occurs for ALL npc merchants, so I cannot trade with anyone in the game. It has also affected ALL of my saved games universally. This is also affected quest progression - I speak to an NPC to progress a quest, but at the end of the dialogue, a similar glitch occurs and the quest will not move forward. Anyone encountered this or know of a fix? I'm screwed.

Rebooting PC seemed to clear up the problem. Very strange, because exiting the game and relaunching did not help at all.

Sorry to necro this thread, but I am having the EXACT same problem. Only rebooting the PC did nothing... did a fix for this issue ever surface? I have been googling for days, and found nothing.