OK, I had just finished the quest for getting the pale for Tallius. I fast-travelled to Solitude to save time and entered the city, as soon as I entered the city the civilians started attacking me randomly and then the guards attacked them. This process could not be stopped because a few of the important people could not die. And Tallius was helping them kill everyone. Is this because I am a vampire???
An explanation would help

Yes that is most likely the factor. Since you are in the Legion they still like you and anyone attacking you gives them a bounty. Go feed on someone, then go back again. If that works I suggest you get that vampirism cured.

Being a vampire might explain the townsfolk attacking if you haven't fed in a while I think.

Ok, I will try this. Thanks for the help guys!