Sysem error E73 on Xbox 360
Follow the steps below, Hope this helps
1. Turn off the xbox 360, disconnect the cables wait for 20 seconds reconnect the cables and turn it back on.
2. Remove the hard drive, turn on your xbox 360 without the hard drive.
3. Re attach the hard drive and turn on your xbox 360
4. If the steps wont resolve the issue, your console needs to be serviced. Contact Xbox Customer Support to check the warranty status of your xbox 360.. Good Luck!