kk i repair 360's as a business i have repaired over 200 and only 8 were not repairable i will let you in on the secrets i use in repairing them first try

tools you'll need
1.heat gun about $25 at your local hardware store
2.Thermal paste $5-$10
3.screws and washers for RROD repair
i think that's it

Step 1: take the console apart
Step 2: clean the dust form the motherboard and the thermal pastes form the cpu and gpu with alcohol
Step 3: Put the motherboard on a flat surface and on a spot were the heat gun cant burn the surface
Step 4: start moving in circular motions over the gpu stay about 2 inches from the motherboard and do this for about 20 seconds do the same for the cpu and A(HANA) chip and DONT MOVE THE MOTHERBOARD OR TOUCH IT!!!
Step 5: after its cooled down apply a very small amount of thermal paste i use Arctic Silver 5 its the best you can get know when its applied spread it with like a credit card or something there should be a very thin layer of it it doesn't take much
Step 6: now when it comes to the screws it always best to put the screws on then the washers on the other side of the motherboard then put on the heat sink the washers are used to put some space between the motherboard and heatsink to get rid of board flex
Step 7: put the motherboard back into the metal shell put the fan on and connect the rf board (the thing that has the power button on it) hook it up and test

i really hope this helps you...its really hard trying to explain a repair over a text
HAPPY GAMING 8D