Ok I do not know if this has been posted before but im just trying to help out by getting up some tutorials on how to fix a xbox because I have realised loads of people are posting complaning of a broken xbox.
Why Does it happen?
1.) When the console is getting insufficient power. This can be readily identified and easily fixed without having to open up the console.
2.) The other more serious cause for the red ring of death is overheating of your Xbox. The Xbox overheats because of various design problems.
What to do first if it happens
1)Restart the console.
2)If this did not work, there could be a loose cord or cable. First, any cables and power cords that can be removed should be disconnected. Unplug the power cable from the wall plug. Firmly reattach all cables and cords back into the console. Now connect up the power and turn on the console.
3)If the above step didn't work, then try turning off the console, unplugging the power and then disconnecting the hard drive. Now plug into the power and turn the console back on. If console does not show the three red lights error, turn it off and disconnect the power cord from the wall. Finally, reconnect the hard drive, plug in the power, and turn on the console.
4)If you are using a defective surge protector, plug strip, or extension cord, your xbox may not be getting adequate power. Try plugging the power brick directly into the wall. This sort of thing happens more often than you might think. My DSL connection used to be very unreliable until I bypassed my surge protector and plugged my modem directly into the wall. I should have done this in the first place rather than making a lot of angry (and useless) phone calls to my internet service provider.
5)If you think that your machine has overheated, then turn it off and let it cool down. Ensure that the cooling vents are not blocked in any way and keep your Xbox 360 in a ventilated and open area.
6)Take it to a shop.
Here are some video tutorials (This is not my video):
If none of this is possible for you to do just take it to a shop or buy a new one!
Hope this helped