I decided to start afresh after Hearthfire was released and have noticed that when entering Windhelm the quest characters are standing around the body but the guard is missing and the quest is unable to start. I have reloaded to a previous save and tried again but get the same issue. I switched of my machine and turned it back on but get the same issue.
Before the Hearthfire release this quest worked fine, anyone else had this issue.

Hi, this is a known bug and there is a solution that works *some* of the time. Watch this video and try this out, it worked for me when I had this bug, http://www.youtube.com/watch?v=J5x6wJHHpUM

good luck!

I experienced this aswell! I thought it was because a master vampire decided to attack Windhelm and the vamp killed that guard who stands with the others, appears i was wrong then.

This has been an issue before Hearthfire, there are probably a dozen things that have been known to go wrong with that quest. But I always start the quest as soon as possible upon getting into skyrims' story. That way there isn't much that can go wrong with it hopefully. Also, the guard and other NPCs normally only appear at night.

Thanks for all the reply's will try it later today and report back.

I have tried it again and again at different times all the other characters are still there, dead body , three witnesses but no guard, I have checked all around and found no dead guards or even ash piles, I haven't had any vamp attacks in Windhelm only at Falkreith poor Lod he was the first to die.