Try the following:
If you see a message that your computer can’t connect to the iTunes Store, click another item (Podcasts, for example) and click iTunes Store again. If it still doesn’t connect, make sure your Internet connection is working—open a web browser and visit a website. If your Internet connection is OK, there may be a problem with the iTunes Store. Try visiting the store again later.
Make sure your computer’s date, time, and time zone are set correctly in Date & Time preferences. Choose Apple menu > System Preferences, and click Date & Time.
Make sure your account information is accurate and that you don’t need to correct a problem with a previous purchase. Sign in to the iTunes Store (if you haven’t already), choose Account > View My Account, then type your Apple ID and password. To verify your account information, click Edit next to Payment Type.
Make sure the iTunes Store is available in your country. For more information, visit the iTunes website.
If you can’t find the song or album you’re looking for, it may not be available for sale. Visit the Request Music webpage, and then visit the iTunes Store at a later date to see if the song or album is available.
If you’re still having trouble using the iTunes Store, visit the iTunes Store Support website.