Think you could give us more details? Full system specs? Did you recently upgrade a component or is it a new build? We don't have much to work with here.
sorry ref stupidly description but had to rush out. when just the 24 pin mainboard power cable connected the fans spin and mainboard getting power cos the led on mainboard lights up green. when i connect the 4 pin cpu power cable i just get green light. no fans. its an asus m2a-vm hdmi. had done some work on it recently. is prob a bent pin or similar. end of day new mainboard not massive expense but i like to exhaust most possibilitys