Hi! I think this solved it! The Northbridge was wiggly (the plastic screw under the cpu had melted).
I followed your link. Here is a short of what I did if anybody with the same problem finds this thread.
0.5 Download Istat Menus and see if the I/O Hub Tiode is very hot. If it is, feel if the Northbridge is loose.
1 - I removed the CPU heatsink. (one turn at each screw, then over to next screw until all where loose.)
2 - I dragged the plastic screw out with a wrench (not sure this is the way to do it, but it worked fine.(
3 - I removed the thermal compound with ArcticClean thermal remover (couldn't get it all away though). Also read that alcohol will work.
4 - I attached new thermal paste.
5 - I screwed back the Northbridge with metal screws (just found some that fitted kinda good from the garage, there are probably some that works better...)
6- Gently screwed back the heatsink on the CPU. One turn at each screw until they started to tighten)
7 - Computer wouldn't start...
8 - I screwed the CPU heatsink gently tighter. (be careful, but I was a bit careful at first, that's why it didn't start). Better to be too careful and just tighten a little more until it starts than go all in and risking breaking your CPU.
9 - Done! Works great again. Now 75 Celsius instead of 128(!).