Apple:

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.

And:

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.

Not sure which Apple TV model you have? Here’s a helpful guide. Note that the 1st gen Apple TV is silver.