I had the same thing happen to me the other day. I unplugged my 28" monitor which is hdmi and then after that could not get any signal to it after that even with a reboot. I used remote desktop to get into the vista machine and the stupid ati CCC wont load under remote desktop so I couldnt even see inside there to check to make sure the drivers didnt turn off the monitor somehow. I ended up booting into safe mode and doing the vista system restore to a point about 6 hours earlier and it fixed the problem. I am guessing that the drivers are the culprit for you as well. These drivers are ass for now until they issue a proper set for these cards. Try doing a system restore and if you cant do that then remove all of the drivers from within safe mode and then run driver cleaner. reboot into windows and then reinstall the drivers and you should be good. I dont think you have a bad psu or card or else you wouldnt get any video during post or in windows safe mode.
edit: i see you fixed it. great!
edit: i see you fixed it. great!