If you want to hack your Xbox 360 and your dashboard version is over 7371 then the only way that you can hack it is with the reset glitch hack (RGH). 
When I started looking for a way to hack my 360 I heard about the jtag method only to find out that my dashboard was newer then 7371, but in early September a hardware exploit was developed know as the RGH.
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Basically what the RGH does is send a single to the processor that tells it to reset. Usually it would do exactly that however if the single is sent when it is booting up it allows us to run unsigned code. To perform this RGH and utilize the exploit what you will need to do is read the NAND, install the modchip, write the NAND and installing your dash board of choice (i will be using xexmenu). To do this you will need: modchip (i will be using the coolrunner from team-xecuter) coolrunner LPT program cable male LPT port (printer cable) (x1) wires (x12 this will be your LPT cable so make them long) computer with a female LPT port a program to read the NAND (i used nandprob 2 you can find it ) soldering iron solder Jtag tool (software) 360gcprog (software) flux (not needed but HIGHLY recommended) ***Disclaimer: I am not liable for any damage that may be caused to your property or self from following the instructions in this tutorial. Soldering irons can be very hot and cause burns, as well as possibly break your Xbox 360. Opening your xbox 360's shell will void its warranty. *** now then lets get started.
First you need to completely take apart you 360 there are plenty of guides to do that so i wont cover it here. When the case is removed it should look like the picture. I highly suggest that you take off the metal case it sits in so that you can access the bottom of the motherboard.
To read the NAND, which is basically the Boot Sector of the Xbox 360, you will need to solder cables to the motherboard in very specific spots. To find those points use the diagram in the first pictures, make sure you find it on the xbox, and flip the motherboard upside down making sure you can see the bottom of the points that you are going to solder to. I suggest flipping the motherboard upside down because the points are small bumps of solder removing any need to add external solder. I also put the resistor leg on the motherboard because they were easier to solder in to place. So if your soldering connections are strong and not overlapping anywhere then we are ready to read the NAND. Open and install nandprob and restart your computer.