I had a problem like this after 4 days with my 2.7ghz w/ 460. I was using spotify and lightroom and the system completely locked up. I did a hard shut down and rebooted. Started up Lightroom and it locked up again. This time when I did a hard reboot, it would come right back up to where it froze upon me putting in my password. I called Apple Support and we tried to reset everything (power, macos, nvram) but nothing worked. After about 3 different calls/techs, it was determined the hard drive was corrupted so bad it couldn't be recovered. They sent me a label to ship mine back and they built me a new one. Took 2 weeks to get the replacement after waiting almost 7 to get my initial one.
You might want to give them a call.