No Chime, Black Screen after High sierra update
After not using my old iMac for a long time I turned it on and it was working fine (with OS 10.6.8) . I successfully upgraded it to El Capitan (after changing the date to 2016 in the terminal). iMac still working fine after the upgrade, then the same day i decided to upgrade it to the latest available software (High Sierra). Update going fine up until the automatic reboot, I could hear iMac rebooting (no chime though) and the screen stays black.
After restarting it a couple of times I tried PRAM reset, but i noticed the wireless Keyboard and mouse aren’t connecting (green led keeps blinking for about 3 min). I also tried with a Windows USB keyboard with no results.
I also tried a SMC reset but it didn’t work.
I tried to connect the iMac with a VGA cable to my TV but it didn’t work (with my MacBook Pro it connects immediately).
I removed the screen and when booting the iMac I noticed that the first 2 diagnostic LEDs are ON (1st is always ON), but the 3rd and 4th are not.
I tried to “bake” the GPU (AMD 109-B98557-00) in the oven for 10 min at 190°C/374/°F), also with no results.
What could be the cause of this issue? The computer has been working perfectly until now. Should i buy a new GPU?