I have tried to install Ubuntu 11.10. During the installation process the CPU fan was switched off. Some minutes later the notebook switched itself off.
How could I switch the fan manually on?
Are there other options?
boot the installer with the switch
You should find that the boot cd has other options and some of these relate to power (usually accessed by Functon keys).
Disabling acpi will remove ubuntus ability to interact with the systems power management.
Also check the bios. Some systems have accelerators for graphics and cpu (like cruise control or load sensing overclocking).
Many of these were designed to work with Windows and do not conform to normal standards. Try disabling these by elimination.