CPU fan only spins during POST

Got a laptop here, an RM nBook 2500 (CY25). The machine boots, and works fine.
The CPU fan will come on at startup, and will stay on until about a second before the RM splash screen appears.
After this it will not spin up again. The PC will continue to boot to XP and will turn off shortly after reaching the desktop due to overheating. The fan is not blocked, I have cleaned out the HSF and applied new thermal paste. The fan can move freely and as I said earlier, initially it starts up fine, making me think it may not be the fan. There is nothing fouling the connector on the board. There are no BIOS settings related to the fan or anything similar, and I have tried changing each setting.

Seems a shame to throw this PC out because of this as it's a nice little laptop, and everything works apart from this. Anyone got any solutions for this?

My only thought is that the sense wire on the 3-pin connector (goes black, yellow and red - methinks yellow is the sense wire) may be loose at one end. I can't see it being but the fan does get power so obviously the other two must work. I may have another fan off an old Toshiba that can sacrifice its connector.

It's a long(ish) shot, but try a CMOS reset.