text: cant power new built computer when cpu is powered on? i just recieved a brand new computer parts from this computer olympics (mobo, cpu, case, power supply, ram, etc.) and i put it together and for some reason i can power the mobo on and get the fans spinning only when the socket 775 cpu's little 4 pin power cable isnt in. not the cpu fan power but the cable from the power supply to the mobo for the cpu.  do u think the cpu is bad? what model intel cpu is it and what model motherboard is it?  have you connected the power switch correctly. just because the board gets power when you press the button doesn't mean it's in the right place. i connected the power button wrong once and the pc would always go on but would not post properly. put the switch in right and all was well. try that otherwise the board might be dead, there is a possibility that something might be wrong with the powersupply.