Ok so i was going this quest and i killed some dude who teleports all around the place i killed him while he was in the middle of a teleport there's the arrow icon there but there nothing there im on the 360 so no commands is there a way of abandoning a quest and restarting it?

anyone?

Reload.

i overwrite it by mistake

Had the same problem with a Stormcloak quest. Had to free prisoners in this fort, but the cages they were locked in simply weren't there. Therefore I couldn't free them and couldn't finish the quest. I tried killing the prisoners and doing the rest on my own. That turned out to glitch too. SO I can't finish the Stormcloak quests anymore and the civil war will never be won by any side. Pretty unfortunate if you ask me. And if I go back to Ulfric he just tells me to finish the quest and I can't.

I tried reloading and it still messed up. So I really have no idea. Is it a main quest? Do you HAVE to do it? If not, then don't finish the quest. It's unfortunate but the only answer.