When you run into a situation where the computers that you once used with your iTunes account are no longer accessible (e.g. if dead or sold on), you might think that you can just keep authorizing new ones. However, there is a limit on how many you can have linked to your Apple ID at any one time — this is currently 5. After this, no more computers will be able to be associated with your account and therefore won't be able to access the iTunes Store.
But, what happens if there are computers linked to your iTunes account that you can't directly use in order to deauthorize them?
Normally the only way to deauthorize computers is to work on each one via the installed iTunes software. However, for ones you can't access you obviously won't have this luxury. In this case, the only way to deauthorize them is to reset your account and then add the ones you own back again.
By following this guide you will learn how to remove all computers in one go that are associated with your Apple ID using the iTunes software. However, before proceeding keep in mind that this is a last resort and can only be done once per year.
Deauthorizing Old or Dead Computers
Launch the version of iTunes installed on your computer and apply any updates if necessary. Now choose the version that applies to you and follow the steps below.
Sign into your iTunes account by clicking on the log in button (image of head and shoulders). Type in your security information (ID and password) and then click the Sign In button.
Click the drop-down arrow next to the head and shoulders icon and then choose the Account Info option.
Now type in your password again to access your private information.
Look in the Apple ID summary section.
Click the Deauthorize All button. This will only be available if you have at least 2 computers linked to your account.
A message should now be displayed that all computers have been removed.
Click on the iTunes Store link in the left window pane (in the Store section).
Click the Sign In button near the top right-hand side on the screen. Type in your Apple ID and password in the relevant fields and click Sign In.
Click the drop-down menu next to your Apple ID name (top right-hand side of screen as before) and choose the Account option.
On the Account Information screen, look in the Apple ID Summary section for Computer Authorizations. If you have 2 or more authorized computers you should see a Deauthorize All button displayed — click on this to continue.
A dialog box will now pop up on the screen asking if you want to remove all computers associated with your Apple ID. To proceed, click the Deauthorize All Computers button.
Finally, a message should now be displayed verifying that the deauthorization process has been completed. Click OK to finish.
Re-Authorize All Your Existing Computers
You will now have to re-link your existing computers with your Apple ID account by using the Authorize This Computer option. This is found in the Store menu at the top of the iTunes screen.
More on Apple's iTunes Authorization
If you are not sure what authorization in iTunes is all about, then the following section briefly explains the nuts and bolts of this feature without going into too much technical detail.
In order to use the iTunes Store and the content purchased from it, you have to ensure that your computer is authorized via the iTunes software application. The idea behind authorization in iTunes is to make sure that the digital products that have been downloaded from the iTunes Store are only accessible by the users who have legitimately purchased it — this includes the ability to transfer your iTunes library to a new computer etc. This DRM system as it is often referred to is designed to limit the unauthorized distribution of copyrighted material.
To be able to access and manage content you have purchased from the iTunes Store, your Apple ID has to be linked with every computer you use. Doing this will allow you to play media content such as music, audiobooks, and movies. Other types of content too like iBooks, apps, etc., can only be managed via an authorized computer. If you intend on syncing all your iTunes Store purchases to your iPod, iPhone, etc., then you will have to ensure that the computer you are working on is authorized.