T420 Thermal sensing error

[xeleron]

First of all hello forum members and thank you for having me in.Without further introductions, here is my problem.I own a "state of the art" Lenovo thinkpad t420 (i7 2620m 8 gb ddr3,Quadro nvs 4200m, 500 gb seagate 7200 rpm hdd,intel 6300 agn ,bt,ericsson 3g card, fingerprint reader,1600x900 LCD,and the 9 cell battery) and I have a serious problem with it.This morning,when I started it,it showed a weird "thermal sensing error" and it would then turn off. I have tried restarting it,resetting the bios,but nothing helps.Is there any way I could revive it, or ,as google says, I have ro replace the motherboard (expensive)?Thank you.

[RealBlackStuff]

Welcome to the forum.
When was the last time the thermal paste between CPU and heatsink was refreshed?
If you don't get a "Fan error" it could be instant CPU overheating that causes that error.

[xeleron]

Oh,I'll check him right away (i got really angry because I always had the impression that Thinkpads are very reliable,and he abandoned me when I needed him the most).I do have a fan error if I actually disconnect the fan (one of the solutions found on the internet was to disconnect the fan and reseat it-of course,unplugged).I could try thermal pads if you consider them necessary,although from my memory (not the first computer fixed,and certainly not the last) the last time I greased him there were no paddings.

[RealBlackStuff]

NEVER use thermal pads!
Get a decent thermal paste, like Prolimatech PK-2 or PK-3, or Thermal Grizzly Hydronaut or Kryonaut, not some cheap junk from the corner shop!
Make sure to clean off the old paste first!

[xeleron]

Just tried it, without pads,new grease,and yes,I have cleaned it before,unfortunately,the same error.I even tried reseating the CPU (took it off,stared a bit at the socket and the pins,all seem fine).Someone suggested (on another forum) that I should try another CPU on the motherboard,implying that it might be a failing CPU,however,this seems quite a long shot.I could try it,but unfortunately the only Sandy Bridge CPU that I have at my disposal is an Intel i7 2670QM which is not officialy supported by lenovo (I've read that some systems do work with it but with turbo core disabled and that it heats up quite fast given the extra 10W TDP it has over the 2620m),and I fear that I might do more harm than good to it.

[RealBlackStuff]

Try unplug the fan, the replug it in.
If no improvement, try another CPU or start looking for another motherboard.
I'm out of ideas at the moment.