Instructions
Disconnect all cables, controllers and peripherals from your Xbox 360. This includes Wi-Fi adapters, hard drives, Kinect, memory units and HD-DVD attachments.
Ensure that your Xbox 360 is in a well-ventilated area and not enclosed in a cabinet, as excess heat contributes to issues such as the E74 error.
Reconnect only the power and AV cable to the Xbox 360 after they have been disconnected for at least 1 minute, then power the Xbox 360 on. If the unit powers on with no problem, turn it back off and reconnect your peripherals as your unit was only experiencing a temporary issue. If the E74 error is still present, you need to set up a console repair.
Call Microsoft at 1-800-4MY-XBOX (1-800-469-9269) to schedule a repair. Alternatively, save yourself the trouble of waiting on hold by using email support (see Resources).