How To: Deauthorizing A Dead Computer For ITunes
First, you need to be on a computer that has iTunes. First sign in and go to the iTunes store. Then go to View Account. I had to do this by clicking on that top corner button with my iTunes id.
Where it lists how many computers are authorized on this account, there's a button that reads "Deauthorize All" that you have to click.
Yes, this means you'll have to reauthorize all of the machines you want to be able to play your music, but it's the only choice when you have one [or more, like me] computers dead to the world.
Note: You may only use this feature once per year. The Deauthorize All button will not appear if you have fewer than 5 authorized computers or if you have used this option within the last 12 months.