The iTunes Store lets you hear short clips of music and audio books and lets you view sample clips of the music videos and movies it offers. When you play a clip or browse items in the iTunes Store, iTunes saves the data in a cache file on your computer. If you stream a lot of clips, the cache file can become large. The cache file could also cause stability problems with iTunes if the cache becomes corrupted in some way. You can reset the iTunes Store cache from the Preferences.
Video of the Day

Step
Open iTunes, and then press the "Alt-X" keys to display the menu bar.
Step
Open the "Edit" menu, and then select "Preferences."
Step
Click the "Advanced" tab, and then click the "Reset Cache" button beside "Reset iTunes Store Cache" in the bottom half of the window.
Step
Click "OK" to close the window.