It sounds like the box overheated. There is a troubleshooting sequence here: http://support.xbox.com/en-US/xbox-360/console-power/xbox-360-no-power-solution , but it looks like that's going to simply tell you that your xbox needs service. Is your console still under warranty? If so, I would recommend sending it back to have it fixed. If not, try re-flowing the motherboard and putting new thermal paste under the heat sinks.