Problem with The Dark Side

[Aniutkaa]

Hi everyone, what's up?

I play The Dark Side since a while and I think I screwed up a bit the things. I got to Montville and I killed the guard who was infront of the king's gate ( where the zombies are) and then I found out that I need this guy to complete the Montville quests. The worst thing is that I saved the game once or twice so I can't load it before killing the guard.

What I can do? Is there any way to get to a oldest save or I must start it again?

Thanks!