The motherboard has no way of knowing how fast the power supply fan is running. So the problem fan must be the CPU fan. Some CPU fans run too slowly when the heatsink is cold and so trigger the fan warning. Often it is possible to override the fan warning in the BIOS.
The computer doesnt stay on but 15 seconds, so I am unable to do anything nothing . Both fans run at the same time when turned on and both fans turn off at the same time. So I am unable to determine which fan is causing the problem.