Not sure if this is a motherboard problem or not

Here is my problem. I built my pc a few years back everything is running fine until this morning. I had a ipod to pc connector plugged into the usb port on the pc. My dog chewed through the cable and my pc shut off. This is what I have done so far,
I unplugged the power, waited then plugged it back in. The computer will turn on but there are no hard drives turning. All the fans in the pc are working and turning.
The original power supplies fans were not working, so I bought a new power supply and plugged it in, works fine.
My dilemma is not knowing if I should get a new motherboard or not. Like I said, the fans will start up but I don't hear any beeps such as when the actual operating system starts up and the hard drives are running.
The monitor turns on but goes right into a power save mode and shuts off instantly.
Please Help .. thanks