Latitude D800 Fans won't Run

I am a refurbisher and rebuild computers for the disabled. I recently received 2 D800 laptop donations.One worked great right away including running Windows 7 Pro. The second system would run for a while and then shut down because of heat. I cleaned the heat sink of a bit of dust, but the fans would not run, except when powered up they (both) would jiggle, but neither would spin up. I have seen some BIOS settings that monitor heat, voltage and fan info, but not the A13 BIOS from Dell.

I finally located a piece of software that allow me to monitor the temperature and manually run the fans, either both or individually. (i8kfangui31.exe) It also allows me to automatically control the fans based on temperature, but when I apply that feature the fans stop running.

 Since I can, now, track the temperature and control the fans, the system runs fine. My question is if the computer detects hot enough temperature to shut the system down and the fans work just fine, why don't the fans work automatically?

Thanks for any ideas....