The Xbox 360 stores temporary game files on the hard drive in the system cache. The system cache can sometimes get corrupt, and can cause some games not to play correctly, or cause disc read errors.
When you clear the system cache, it doesn’t remove your gamertag, however it does remove any game updates you’ve downloaded, and achievements will be temporarily removed. Your achievements will be downloaded from Xbox Live the next time you connect however, and you will be prompted to download any game updates again when you play them as well.
To clear the Xbox 360 system cache, do the following:
1. Go to My Xbox and select System Settings
2. Select Memory
3. Go down to your primary storage device and hit the Y button
4. Select Clear System Cache
5. It will ask if you want to continue, click the A button to select Yes
If the Clear System Cache option didn’t show up in step 4, then from that screen hit the following buttons: X, X, LB, RB, X, X and step 5 should show up.