No power - Apple Cinema HD 30 (A1083)

Hello, I have a Apple cinema HD 30 (A1083). I have no power. I checked the power supply and it is good. I bought a main board from ebay. I still had the same problem so I returned it (minus a 15% restocking fee). I read somewhere that you have to have the usb cables plugged into the computer for it to work. Is this true? If so I may have returned the part I needed to make this monitor work. (just my luck) I bought this monitor for $25 used off craigslist. I am really excited to get this working. I have heard great things about how fantastic the dispay is. I am ready to do some gaming on it. I am an electronic technician but not so familar with this apple monitor. I figured I would turn to this forum to learn from some apple experts out there. Any imput would be wonderful in troubleshooting my problem.

thanks

Tommy