It can happen if the signal is sent, but there's bad connection at the header pins. It can happen if the fan works just fine, but fails to send its speed signal to the header. It can happen if the fan is faulty and truly does not ever start. If that happens, many mobos will not even let you boot up. And that's what it would decide if it gets NO speed signal there. A secondary but vital functioon of the CPU_FAN header is to monitor the Speed signal coming back to it on Pin #3 from the fan for FAILURE. I am assuming you plugged the new CPU fan into that header. Linked thought: did you disconnect and then REconnect the CPU Power cable near the CPU socket?Īnother possibility is a poor connection of the cable to Pin #3 of the CPU_FAN header. Most likely idea is you bumped something else and disconnected it without realizing.
