Why does my iMac turn to a Gray Screen while installing OS El Capitan?
I replaced my hard drive with a 2T HDD also replaced SATA power cable. When I turned on my iMac, I held down the option key and selected my external 1T HDD in a docking station, which has El Capitan installed on it as a boot-able drive. I saw the apple logo appear with a generating progress bar and then it switched to a blank Gray Screen for an hour. I could hear the fans blowing like crazy and my external boot drive was not blinking progress anymore. I think it is a hard ware issue but not sure whether I should replace GPU or something else. I would like to keep this model iMac for a little bit longer because I can’t afford to buy another one. I greatly appreciate any insight or resolution for this.
Is this a good question?
With the external drive disconnected with a USB keyboard plugged in, restart your system and press the D key to enter into the onboard diagnostics did you get any errors?
Reference: Mac startup key combinations
@danj Dan, yes. Error note: 4SNS/1/40000000: TH00-9.000
by Sunflower De