The similar issue happened to me some times, when a faulty USB cable used. I always using isolated dedicated power supply for driving arduino borads after flashing them. Remember! Although most of the USB ports could drive 2Amps, most of the cables are not suitable for this. They will not burn, however from the initial 5V, you will have - depends on the length, diameter and load - 3.5 - 4.5V. Some cases, this amount of voltage drop is enough for making arduino working faulty. More over: Arduino is very sensitive for EMI. If you feeding it with large signal while you are flashing it, you can easily kill the board as well. And at last, you have to take care of the Vpp should not exceed 3V.

Cooler Master Hyper 212 EVO uses 4 pin header and in desktop mainboards, 25KHz is used for PWM frequency. You need to adjust the frequency to 25KHz in the code. That's all.

Dear Friend,

Your project is very good! I just used your code and built a similar stuff but with a two lines of LCD display. I have some doubts about the accuracy and representation of the frequencies, but your code is far better than the others I tried.