No solution in this video other than reformat. I did a Yosemite update and didnt really use my iMac for a while after the reboot. I then had this white screen with a black cursor, which i then discovered is known as the gray screen of death or the white screen of death. I all it white because my screen appeared white. This video is just chronicling what happened to me, the steps i took, in hopes that maybe some of these steps ually will work for you. They didnt work for me. Ultimately i had to create a usb stick that had an installable version of Yosemite. I thought i had captured most of that process but I didnt. Some of it is on here. This isnt really a solution video, but more of a symptom issue.\r
I called Apple, and provided them the error i had, but since my iMac is from new, im out of the service period.\r
I think that is a little messed up though, considering it was their update that caused my issue.\r
Ive work as an IT Professional for 10+ years, i work on Windows machines, not Macs. But im not about to pay someone to fix a simple issue on my iMac. \r
So i got instructions online on how to make the bootable usb, and reformatted my iMac and am starting from scratch.\r
I store all of my personal files on a network NAS drive so all i lost is software (which can be reinstalled). I dont do the time machine thing.