my new iMac went black

I just got a new iMac and started it up for the first time. Everything was going fine as it was updating the system software and then the screen went completely black. I waited for about 15 minutes thinking it was just taking some time to install the software but it was unresponsive. I tried to power it back on but it won't turn on. I even held the power button down for 10 seconds and still no response.i