Authorized computer

[Europa]

I reinstalled Vista on my laptop and sold it to my sister. I forgot to deauthorize that computer from my iTunes library before reinstalling the OS, so it's still showing as one of the five computers that can play those files on my Apple account. I feel like I wasted one of my five for nothing. My sister doesn't use iTunes at all and doesn't even have it installed on the computer. Is there any way at this point to deactivate that computer?

[acosmichippo]

yes, but you have to wait until you have 5 computers authorized.

http://support.apple.com/kb/HT1420

To deauthorize all computers associated with your account
If you find you have reached 5 authorizations, you can reset your authorization count by clicking Deauthorize All in the Account Information screen.

Click iTunes Store in the menu on the left side of iTunes.
If you're not signed in to the store, click the Account button, then enter your account name and password.
Click the Account button again (your ID appears on the button), enter your password, and then click View Account.
In the Account Information window, click Deauthorize All.
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. If you need assistance on using this feature, please contact the iTunes Store support via email (http://www.apple.com/support/itunes/ww/).