Your error code's 0020 and you've done the X-Clamp fix right?
I've had 2 0020's to date, I could fix one; but not the other.
Okay, my recommendations are as follows:
1. Make sure you only used a small (but not too small) amount of thermal compound paste.
2. Disconnect fans and turn on for 30 minutes - allowing it to "bake".
3. While still extremely hot, tighten the screws
very tight, but whatever you do, don't make them so tight that you end up breaking it.
4. Allow to cool naturally, so don't put it in the fridge or outside, and then - after around 30 minutes, or when it's cold (room temperature) test it. Hopefully at this stage it'll work.
If not continue with steps;
5. Time for the penny fix, see YouTube for details:
http://www.youtube.com/watch?v=asTDsKLVexA
6. Heat Gun fix time; I'll see how you get on with the other things I suggested before even thinking of recommending this...
Good luck!
