itunes

Hey, has anyone heard of itunes? Well the other day I recieved a free song from pepsi, so I go to the website and download this itunes. I picked my song it downloaded fine. I was even able to play it the next day. Then the next day, which was yesterday, I tried to go back and purchase another song and I can't hear anything. Not even the song I purchased. I have the newest version 4.2. And like I said I had no problem withit the day before. Does anyone else have this problem or maybe can help me. I tried to access their tech. support and guess what? They don't have one!!! i posted in the discussion group but that didn't help eithor.