Question : Problem: Laptop cooling problem

I am having problems with my HP DV1000 laptop.
It was overheating and shutting off, and upon closer inspection I found the fan was not functioning.
I dissassembled and found no apparent visable fault with the fan, but decided to replace the fan as a first step. The new fan came on for approx 30 seconds and stopped. It has not run again but seems mechanically fine. Having it looked at by a qualified person is not an option because I live in the 3rd world.
Next step I guess is to find out what triggers the fan, a heat sensor I assume. Is there anything that could be wrong other than hardware? Oh and before I try to test the fan I'd like to know why it has 3 wires red, yellow and black
Hope someone can help please!

David

Answer : Problem: Laptop cooling problem

The yellow wire tells the mobo what speed the fan is running at. (Tachyometer)