If you haven't been to Mzulft in Eastmarch already, you need to be aware of the little game breaking problem that can occur there. (If you're not doing the quest then this will not affect you)
Whilst dojng the quest there, I got to the vault along with the npc and read the journal on the ground to continue the quest. Upon doing this the game crashed to desktop, just like it does if you press alt-F4. No biggie I thought as I've had this happen several times before and reloaded the game and my character.
Just as my character appeared I noticed some strange lines of code in the top right hand part of my screen and then the game crashed properly and the error reporting tool appeared. This is where it got bad. I reloaded the game and tried again, crash. I tried many times, without addons, I used the repair tool and even uninstalled and reinstalled the game and it still crashed each and every time.
The strange thing is I could load into and play my alts with no problems at all, so the problem lies inside Mzulft and that particular part of the quest. I had to ask Customer Services to port me out, which they did in a very short amount of time, that I wished I had gone to them first (Thank you).
So if you go inside Mzulft, you do so at your own risk.