Q: itunes won't launch

Does it open in another user account?

Are you seeing any error messages?

You can use one of these documents to break down a user-specific or system-wide problem.

iTunes for Windows Vista or Windows 7: Troubleshooting unexpected quits, freezes, or launch issues

iTunes for Windows XP: Troubleshooting unexpected quits, freezes, or launch issues

No and No

There is another thread about this too. Here is the link:

Re: iTunes won't launch ...

for info.