Just bought a refurb iMac 27 inch with 3.4GHZ i7. I go to turn it on this morning and hear the chime then it goes to the gray screen and then black. I let it sit on the black screen for 30 mins before I shut it down. Tried again but holding shift to put it into safe mode and nothing just black. Just needed to vent. Apple said take it to the nearest authorized service center and see what they come up with. I knew I should have bought a new one instead of a refurb.