The only way to start it that i can think of is to spawn in a windhelm guard via console command and make sure he isnt fighting the imperial guards by using voice of the emperor (can also be aquired from console commands) or any other calming spell and try to talk to him to see if the quest will start that way. Unfortunately there is no way to start the quest if the civil war bug occured in your game (Which it has since you finished the civil war on the empires side and now cant start the quest).
Originally posted by Zivin:Blood on Ice is notorious for being litterally the most bugged quest in skyrim (It has about 30 known bugs and only 2 have been officially patched).
