Seagate Desk, No LED, keeps cycling

When i plug in my Seagate FreeAgent Desk external drive in the electrical outlet only [without connecting it to the USB], it will cycle up and sound like it spins down and clicks. It repeats this over and over, and when i plug it into my USB, it keeps doing the same thing. There's no LED on my Seagate at any time and my Vista doesnt recognize the drive at all. Other USB devices have no problem and my FreeAgent was working great up until a few days ago. Could i need to try a new power cord for my FreeAgent or is it toast? please help?

Thanks for your input. I tried connecting the USB port first and found out i was wrong about its behavior. My external spins up and clicks as it spins down whenever the USB cord is attached to the back of it. It does this even when the power cord is not connected to my external and not connected to my laptops USB port. But this is confusing because i thought power had to go to the unit, either from a USB port or an electrical outlet, for it to spin up or down.