What do you do when iTunes dosent work?

The same exact thing happened to me yesterday. I contacted apple.com and they called me back today. I was told to follow some instructions found in their website and if that doesn't work to call them back and that they would dig further into the problem and try their best to help me figure it out. Anyways, go to apple.com, then clic on SUPPORT and then on the search tab type TS3074. A whole set of instructions will show up and you need to follow them. Hopefully it will work for you, I haven't tried it yet. Also, you can go to their website and under "contact us" you can request for someone to call you as a specific time and help you resolve the issue.