The "Red Ring of Death" is a major hardware malfunction within your Xbox 360 that causes it to essentially crash. It can be identified by three quadrants of the system's power circle flashing red instead of their normal green. Your Xbox 360 should shut down as soon as this happens, and you should not be able to turn it back on, depending on the situation. It can be caused by a failure of one or more hardware components or from not recieving enough power from its power source, which can be fixed without contacting Microsoft. For more information, here's a link to a pretty helpful page. "Wikipedia - 'General Hardware Failure' errors." It should take you directly to the section of a Wikipedia.org article describing the "Red Ring of Death" as well as other Xbox 360 hardware problems. It also has a few solutions for any issues you may have with your console.