How can I spin an old HDD motor?
Most of the HDD motors are BLDC (brushless) motors. They can be driven by brushless ESC. Cheapest would be to buy hobby RC ESC and drive it by PWM. Something like this would be fine. (turnigy plush 25A). 

25A means that it can be used to run motors up to that current without damaging ESC. You could find lower current ESC as well (but this one is cheap enough).

ESC consist of three wires, there are no 4 wires ESC. You need to measure resistance between pairs of wires and connect only wires with higher resistance. One with lower resistance leave unconnected.