Sensor problem

I have sony s480 and its temperature sensor is showing something under real temp.
On ideal use, with a digital thermometer I measured cpu temp from it heatsink, and it show around 66 degree centigrade but the mobilemeter software show 20 degree!
I tried several softwares but they show same temp. Also, I’ve tried updating bios but no thing changed.
In details, I can say its frequenting around 1 degree (yes 1!) and 35 degree sometimes, but right now its 8~5 degree.
Here is a big problem, and it is: when and just when cpu temp gets over 50 degree, the fan start. So the fan is all time off and the real temp going up and up.
How ever I’m using zalman cooler right now so it can’t over heat.
But I know if this keep continuing, my notebook will definitely fry.
I really don’t know what to do with this problem.
Another thing I have to say is that few days ago my notebook was in a bit moistly whether and after that this hell happens.

 

Someone please help.
from minuets ago temp monitor show just 1 degree and dont change!

 

I solve it!
I just opened my notebook and cleaned dusted area near cpu!
thats it.
now it work like past very well.