I can enter Dragons Reach from the dungeons, but if I try to go through the main doors the game will CTD.

I have verified files and gone about my business for hours without any problems, I have also saved it many times so it's not a bad save, but as soon as I try to go through those doors, bang! CTD.

A very strange bug indeed.

Wait inside Dragons Reach for 31 days. Then exit from the main doors, and enter again and see if that works !!!!

But it can be related to some mods you propably have (?!) (For example people have stated that Alternate Start - Live Another Life mod can cause CTD's when entering Dragons Reach !!!!! )

Or maybe some sequences of certain events can cause a crash !!!!

See here: http://skyrimforums.org/threads/load-screen-crash.6100/