Question: After installing Ubuntu 12.04 my CPU temperature gets abnormally high: 80-86 °C. I saw that the CPU fan isn't running. Is it possible for this problem to be caused by Ubuntu or not?

Answer: 
I don't think it caused by Ubuntu. Please check

* Your BIOS setting.
* Reset it to default.
* Update your BIOS.

It it does not work then you have problem with your FAN. (I think)!

Please let me know the update.
When my laptop g6 does that I took a needle and rotate it manually then I start the computer again and it works again, it happen twice now.