iTunes for Windows Vista or Windows 7: Troubleshooting unexpected quits, freezes, or launch issues – This article provides some general suggestions when trying to troubleshoot an issue where iTunes for Windows Vista or Windows 7 won’t launch or unexpectedly quits or freezes. It may be useful to print this document before following the steps outlined below.
For a discussion of troubleshooting iTunes for Windows in Windows XP, see iTunes for Windows XP: Troubleshooting unexpected quits, freezes, or launch issues.
If you are having trouble installing iTunes, see Trouble installing iTunes or QuickTime for Windows.

http://support.apple.com/kb/TS1717