I completed the Battle for Windhelm quest before activating the Blood on the Ice quest and now the Blood on the Ice quest cannot be activated. This is kind of annoying since I NEED to complete that quest before I can buy a house in Windhelm and become a thane.

Hmm same house I am trying to buy ...

I got to the point where I was told I'm able to buy a house in the city, but the guy just keeps telling me something happened and I cannot buy it yet. After some searching on the web, and I think it might be bugged for me too

Same that freaking quest will not start no matter what I do.

The best way to get this quest to initiate is to head strait to whiterun stables after excaping, then pay for a lift to windhelm. Once in windhelm, talk to the caption that hangs out in the market, then look for viola, and after she finishes saying her line about "beware the butcher", fast travel to riverwood, fast travel back to windhelm, go to the cemetary and see if anyone is there, if not fast travel to riverwood again and back to windhelm and look again. Repeat until they show up, it can take as little as 2 time, and as many as 5. Once they show up in the graveyard go talk to the guard, offer to help, then talk to the people standing around, talk to the guard again, and futher offer to assist, go talk to the stewart then talk to the guard again. after talking to the guard, follow the blood trail to the house (north west corner), go talk to the stewart again asking how to get in house, then go talk to the mother, choose the middle option about investing the murders, she'll give you the key. you can then get into the house and investigate everything. pick up one pamphlet about the butcher at least, both journals, and the strange amulet, go talk to viola again, she'll tell you to talk to the stewart, dont do it, go strait to the mage, after talking to the mage, go back to the shop area (where the blacksmith is) stand in front of the guard, wait for the butcher, if he doesn't show right away, wait 1 hour, and he'll be there, try to kill him before he kills the lady. take his key, go to his house, get his journal from the trunk, and THEN go talk to the stewart, and that will be the end of the mission.

This is the method I use to be able to complete the quest, it hasn't failed yet. After that you dont have to worry about any of the other 4 missions colliding with the people involved directly and indirectly with the quest dieing and you'll still be able to buy the house. if you join the stormcloaks, and did all the in town quests (6 total) you will be able to get the house one mission AFTER taking whiterun. If you join the imperials, you will not be able to buy the house until you've taken windhelm no matter how many of the in town quests you do, or stewart quests you do.

I highly suggest to not deviate from the questline (blood on the ice) until you have completed it, else it may become broken, even if you just need to talk to the stewart. Once you enter windhelm for the first time, its best to get the quest and complete it before doing anything else, but i do suggest the above method if you've had trouble with mutliple characters not getting it to prevent it from happening in the future.