I'm stumped. Yesterday morning my computer was working fine. I stepped away for a few minutes, and when I came back it was on a black screen of death saying "Reboot and select proper Boot device or ...

My 27'' iMac was delivered less than 20 hours ago and I immediately set to: By this time it was time to get some sleep so I shut down the iMac. and this morning when I tried to start it again i can ...