The itunes store is unable to process purchases at this time
I have had this issue for about 3 weeks now. What do I do?
Are you using a device or a computer? Can you sign in? The below is for the App Store, but gives somethings you can try.
Connecting to App Store Problems
Connecting to App Store Problems (2)
If necessary, contact iTunes Support. Scroll to the bottom of the page in the 2nd link.
The itunes store is unable to process purchases at this time