If iTunes is acting up, you may need to download and install a fresh version of the program. The latest version's always waiting at www.apple.com/itunes/download. The program itself may also alert you to a new version—or you can make sure it does in the future:
If you use iTunes for Windows, choose Edit→Preferences→General and turn on "Check for updates automatically." If you prefer to check manually, choose Help→“Check for Updates”.
The Mac's Software Update program is designed to alert you, via a pop-up dialog box, about new updates for iTunes. If you've turned Software Update off (in System Preferences), however, you can run it manually by choosing Software Update from the Apple menu.
As with any software update, once you download the software, double-click the installer file's icon and follow along as the program takes you through several screens of upgrade excitement. If the version of iTunes you're installing is newer than the one you've got, you get Upgrade as a button option when you run the installer—and it usually takes less time to do the job.
If you're reinstalling the same version of the program, the iTunes installer may politely ask if you want to either Repair or even Remove the software. Choosing Repair can often fix damaged ...