I've installed Ubuntu 16.04 but my PC starts to run fan at maximum speed when I log in. Once installed I tried to find where the problem is, so I have installed lmsensors, fancontrol and psensor. All temps are o.k. (about 30 °C) but fan speed is -1 RPM (on Windows and on Ubuntu 15.10 fans work correctly). Changing video driver (from X.Org to nVidia driver) fans work correctly (and on Psensor fans are about at 2200 RPM) but my battery runs out quickly because of the nVidia Geforce GTX 960M. If I go back to X.Org video driver the problem returns. I have tried to install laptop-mode-tools too, but the problem remains. How can I solve this problem and continue to use X.Org driver? Thank you so much and sorry for my English.

P.S.: this is the result of sensor using nVidia driver

acpitz-virtual-0
Adapter: Virtual device
temp1:        +38.0°C  (crit = +103.0°C)

coretemp-isa-0000
Adapter: ISA adapter
Physical id 0:  +39.0°C  (high = +100.0°C, crit = +100.0°C)
Core 0:         +36.0°C  (high = +100.0°C, crit = +100.0°C)
Core 1:         +36.0°C  (high = +100.0°C, crit = +100.0°C)
Core 2:         +34.0°C  (high = +100.0°C, crit = +100.0°C)
Core 3:         +34.0°C  (high = +100.0°C, crit = +100.0°C)

asus-isa-0000
Adapter: ISA adapter
cpu_fan:     2100 RPM
temp1:        +38.0°C

EDIT:

I have solved my problem installing Linux kernel 4.6.0 (Ubuntu 16.04 has Linux kernel 4.4.0). Here's a guide to install it and here another solution for my problem (tested) that use Linux kernel 4.3.5.

The second solution slow down system start, so I have used the first one

Solution 1:

Just for the record, since I have no interest in using the intel gpu, I never have. As an experiment, I used the nvidia gui to change to intel, logged out, and, after login the same fan issue occurred in 15.10,

uname -a
Linux deblap2 4.2.0-36-generic #41-Ubuntu SMP Mon Apr 18 15:49:10 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

thus, as far as I can tell, it is not ubuntu 16.04 specific, and, in the various distros I attempted to install on the laptop, including debian, manjaro, mandriva, it has universally occurred, except that only ubuntu 15.10 installed correctly.

Also more interesting, I could not then revert by using the nvidia gui, as after logout touchpad froze, and I need to hard shutdown.

this is interesting as the problem with the power switch was the main reason i ended up with ubuntu, as ever other distro I tried had the issue that the power switch and the commands reboot and shutdown did not work as expected.

I thought it was a kernel version issue, or my laptop, same as OP's, or elan or evdev, or coretemp, but even though arch recommended adding lmsensors and coretemp, coretemp is loaded. thus, the post and answers bring us one step closer, as the issues are somehow gpu related.

best

M