A corrupt iTunes library prevents the iTunes program from opening and prevents Apple device synchronization. According to Apple, the iTunes library must be rebuilt, which resets the library and removes the current content in the media manager. Back up your media prior to recreating the library, as the recreating process erases all content and your Apple device will synchronize with the blank, recreated library and erase the device's information.
Insert the DVD-RW disc into the computer's DVD-RW drive, and open iTunes. Click "File," "Library" and "Backup to Disc." Select the iTunes library and playlist backup and click "Next." Eject the disc after the backup completes, and close out of iTunes. Move "iTunes Music Library.xml" from your iTunes folder to the desktop. Right-click "iTunes Library" and click "Delete." Launch iTunes and click "File," "Library" and "Import Playlist." Locate and double-click the iTunes Music Library.xml file. Insert the burned disc into the DVD-RW drive and click "Restore." or Fix iTunes if It Won't Open on Your Computer
b> You've clicked and clicked and clicked some more, but iTunes just refuses to launch. A non responsive program is frustrating to any computer user, but especially if all you want to do is listen to some music or download a new album. If iTunes isn't opening, there are many possible causes for this error. None of these fixes will affect your current music collection. Though you may need to tweak or reinstall some software, your MP3s will stay right where they are.
Confirm that your Apple device is connected securely to your computer. If you are not trying to access iTunes via an Apple device, or if your device is connected correctly, continue to step two. Configure your firewall to allow iTunes to connect to the Internet. Many firewalls block software programs' ability to get online as a security precaution. This is because some spyware and malware is designed to transmit personal data from your computer. Making iTunes a trusted program within your firewall software is necessary for it to function properly. Create a new iTunes library file. An unstable or corrupted library file can cause iTunes to suddenly quit or not open at all. Recreating a library file is a lengthy process that depends heavily on the operating system you are using. See the iTunes Support page under. http://support.apple.com/kb/HT1451
Reinstall iTunes on your computer. If no other troubleshooting steps are successful, then the fastest way to solve the problem is to start from scratch. Hope this helps.