Hello, I have a gigabyte GA-965P-DS4 motherboard, with Intel Core 2 Duo E6600 CPU and the stock fan of intel that came in the box with the CPU. The fan is connected with 4 wires to the motherboard. The fan sometimes stops rotating, and sometimes it'll be in a state where it rotates for a second, then stops a second, then rotates a second again, and so on for a long while. Especially that last thing worries me. What worries me more is that, if the fan is doing that, when I touch the wires of the fan, the fan suddenly rotates continiously, as if there's a bad contact in one of the cables that gets fixed for a while if I move the cables a bit. Does the motherboard CPU combination I mentioned, automatically control fan speed depending on the temperature of the CPU? If that is so, can it happen that when it's at a border between hot and cold, it'll go in this state where the fan starts/stops spinning every second? Does anyone know what the function of the blue, black, yellow and green wire of the fan are? Thanks.

Have you checked your BIOS settings? See if there are settings to control the fan based on temperature. You should be able to turn that off completely too. The wire-touching sounds scary though, but it might just be a coincidence if you're lucky :S

There was a setting for smart control on the motherboard, and when turning it off the fan constantly turns at full speed.

This proves that it's not a bad contact, and I set it to smart control again to make it less noisy :)