Are all the fans spinning? Do you have a working fan connected to the cpu fan header? What are you using to monitor temps. Usually the alarm is for fans not running. If it were a heat build up/high temp reading then the computer would just shut down unless you disabled that setting in the bios but not the monitoring settings. Go into bios and look at the temps and fan speeds. You could have a malfunctioning temp sensor on the motherboard or if your running fan controllers one of those connections might have come loose. But my guess is the "0" rpm cpu fan speed. If your cpu fan is running then just switch to a working fan on the cpu header shut it up.