How on earth can I get the house in Windhelm!
Thanks

This is a tough house to purchase.

You will need to complete the challenging Blood on the Ice quest as well as a number of side quests for the people of the city/helm. If you have joined the Imperial Legion, you will need to complete that quest line before the option to buy is granted.

Also, when you buy the house, the first home furnishings item you should buy is the one to clean up the mess or else you may be stuck with the mess that's inside the house.