How do I switch back to the U.S. Store?

I went to purchase a song and it said that it wasn't available in the U.S store and that I had to switch to the Belgian store. I clicked "Switch Store" and now everything is in euros and it wont let me purchase a normal song from an american artist. It says "Your account is not valid for use in the Belgian store. You must switch to the US store before purchasing." How do I switch back??? This is very aggravating. Thanks for any help that can get me closer.