The red ring of death is when your Xbox 360 shows 3 red lights in the upper left and 2 bottom quadrants of the power circle (when you have your Xbox 360 in horizontal position.) This indicates a power failure in your Xbox 360.
There are 1 of 3 reasons why this happened:
1. Chords connected to the Xbox 360 may have become disconnected, just try replugging in all of the cables and try turning it back on.
2. Your Xbox has overheated from playing too much. Try leaving your Xbox 360 off from anywhere from 1-4 hours. Then try rebooting it.
3. Your Xbox 360 has a hardware failure, there is no way of getting it fixed (at least responsibly by yourself)
When you get the Red Ring of Death, you call Microsoft at 1-800-4MY-XBOX and they will send you a box (dubbed "casket") for your 360 to send back to them for repairs. Make sure you remove your hard drive and any cables so that the only thing going into the box is the 360 itself. Microsoft will most likely only send you a refurbished Xbox 360, not the one you sent them, so your hard drive/cables will be lost if you send those to them.
There are a lot of ways to prevent the Red Ring of Death, and here are some of the most obvious:
1. LUCK - you may have gotten a faulty system right out of the box. Try looking for a 360 with the latest manufactured date to make sure that it is more reliable. (newer ones have a cooler-running Falcon chip in them.
2. PLAYTIME - never play your 360 for more than 6-8 hours in one sitting. This will majorly cause your 360 to overheat, which will likely cause the Red RIng of Death.
3. OPEN SPACE - make sure you have plenty of open space where your 360 is. The other most common reason why people get the Red Ring of Death is because they don't give the Xbox 360 enough room to breathe/aerrate.
4. FAN - if you are really worried about getting the Red Ring of death, put a small fan behind the 360 blowing air away from the 360 so the hot air does not circulate into the back of the 360.
5. HORIZONTAL- store your 360 in a horizontal position (flat) so the disk can play right. The 360s have no support on the disk that will allow it to stay in place while the 360 is on, so the disk may fall from the disk tray when in vertical position, scratching the disk and maybe breaking your 360. Also, this will prevent you from knocking it over and breaking the console.
Good Luck....

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