Q: Updated my itunes and now when i try to open it it says itunes is corrupted and won't start. Help!

Upgraded my iphone 4 to an iphone 5. When I opened itunes it asked me to update to the latest version. I tried to sync my previous phone but it said error transferring, syncing wont start. I upgraded my itunes and restarted my computer. Now when I try to open my itunes I just get a message saying its corrupted and wont open. Help!