For some reason I can't fast travel to certain places without it crashing. Right now I can't go to Markarth or the Solitude stables, and it always seems to be quest-related. I need to go to Markarth for the Dibella quest and Solitude stables for Thieves Guild quest.

Also the game freezes constantly when I have autosaving on, but when I turn it off I can play for a few hours without it freezing.

Why is this? If anyone could help that'd be great.