What is your motherboard model?
Your MB is the same as my old motherboard.
I had this problem before and as far as I remember the solution was in (Windows 8 Configuration) option, I don't remember really but one the three options inside should be disabled. (MSI fastboot) or (Fast boot), disable one of those option and enable the other, save the configuration and the fan should be at back to low speed. It seems one of Windows 8 option was causing a problem with fan controller.