Ok Your 360 has the dreaded RROD.
Now there's a lot of kits on eBay promising you a quick fix
and in most cases they will work.
The big question is what kit is the best one ?
Sellers stressing you must have this you must have that,
Don't use this don't use that Blah Blah Blah.
What ever kit you buy please make sure it has Nylon Washers.

I can't stress enough how important it is to
have NYLON washers against the motherboard.
Even if you buy from another seller buy NYLON.

Fact: The Xbox 360 has no ground earth like a PC.
It has a floating earth system also known
as an insulated earth.

Basically it's a system where the Xbox's
electrical system is isolated from the casings
metalwork.

By using just metal washers the floating earth
system is compromised.

The chances of shorting out the motherboard will
be huge. Just a little static electricity could
fry your board.