If you installed iTunes on a new PC and you would like to sync, download, or play the items you have purchased from the iTunes Store, most probably, iTunes will prompt you to authorize the computer first.
To do that, your PC should be connected to the internet because you will sign in to your account for verification, and remember that you can only authorize five computers with your Apple ID. In case you want to authorize a PC, but iTunes told you that you have already reached the limit, you can opt to deauthorize a PC or all computers associated with your Apple ID. You can check this guide on how to do that.
Authorize a Windows PC in iTunes
You can either authorize a PC before or after you sign in to your account. The procedure is the same.
1. Run iTunes.
2. Go to the Store menu, then click “Authorize This Computer”.
If you can’t see the Store menu, press CTRL + B on your keyboard to toggle the menu bar.
3. A small window will pop up. Enter your username and password, then click Authorize.
4. Presto! Your PC is now authorized.
If you already signed in to iTunes before authorizing the PC, you will see that the items you have purchased are on the Library already, but pending for download. You should click on the cloud icon at the lower-right corner of an art cover to re-download an item without getting a prompt same below since you already authorized the PC.
Do not worry if the Authorize This Computer option was not grayed out after you authorized the PC. As long as you already got a notification same above [step 4], then you are ready to download or play your purchases.
Go here to learn how to transfer your iTunes Library from one PC to another, or between two hard drive partitions without re-downloading your purchases.
Last Updated: May 11, 2015
Tested on: iTunes 184.108.40.206