Windows XP or Vista PCs
Starting May 25, Apple will introduce security changes that prevent older Windows PCs from using the iTunes Store. If you have Windows XP or Vista PC, your computer is no longer supported by Microsoft, and you're not able to use the latest version of iTunes.
You can continue to use previous versions of iTunes on your Windows PC without support from Apple. However, you won't be able to make new purchases from the iTunes Store or redownload previous purchases on that computer.
After May 25, you'll need to use Windows 7 or later with the latest version of iTunes to make purchases from the iTunes Store and redownload previous purchases.
Apple TV (1st generation)
Also beginning May 25, security changes will prevent Apple TV (1st generation) from using the iTunes Store. This device is an obsolete Apple product and will not be updated to support these security changes. After the changes, you'll only be able to access the iTunes Store on Apple TV (2nd generation) or later.
More details in the full support article linked below...