Laptop is HP pavalion dv6000 with intel+ge7400. The CPU fan runs during bios screen+grub and right after linux (ubuntu 9 based mint) starts loading, it switches off. What could be the reason.
The fan probably is running until the daemon which controls it loads. At that point, since the CPU is relatively cool, the fan is not needed, so the system shuts it off. If you do CPU-intensive work like rendering video or playing 3D games, the fan will probably switch back on. Certainly that is how my own DV6000 running Ubuntu acts.