If you receive error code 3CD6 or 80072F8F , your console’s internal clock battery may be dead, or your connection to Xbox Live is blocked. Set the correct date/time manually in Settings, then try again.
If your USB ports are broken or your specific console revision refuses to boot from a flash memory stick, burning the update to physical media serves as an effective alternative. i--- Xbox 360 Dashboard Update Download
The folder must be named exactly $SystemUpdate with the dollar sign included. Lowercase characters or spelling mistakes will cause the console to ignore the files. If you receive error code 3CD6 or 80072F8F