Fans won\'t run; laptop overheats and shuts down

[neanro]

My sister asked me to help her out by replacing a noisy fan in her older laptop. She ended up buying the wrong fan to replace, so I bought the other (there are two total) and replaced both of them. Now, when running Windows, the fans will not run. The laptop ends up overheating and shutting down.

(1) The fans do come on when the power is first turned on.
(2) When I performed a BIOS update on the machine, the fans came on and ran at full power while the flash occurred.

The machine is a Compaq Presario R4000. Part number PX356UA#ABA.

I have tried everything I know to do.

(1) I completely reinstalled the OS (Windows XP Professional).
(2) Then, proceeded to update every driver including those for the Motherboard and Southbridge.
(3) Then, I upgraded to Windows Vista Home Premium.
(4) And, then upgraded to Windows 7 Professional.

To no avail, the fans still do not run while Windows runs, and after some time, the laptop overheats and shuts down.

I have installed FanSpeed at each iteration of installing an OS. FanSpeed gives me the temperature of the CPU, but has no fans listed, so I cannot control the fans using that application.

Any suggestions?

Thanks,
Neil

 

[kenrivers]

Have you checked the exhaust ports for the fans and heat sink to make sure they are dust free and nothing is blocking them? When in use is the laptop elevated so there is good air flow? Another alternative is to try a cooling pad.