iMac screen shows nothing after replacing hard drive I replaced the hard drive on my iMac 8,1 (iMac 20-Inch &quot;Core 2 Duo&quot; (Early 2008)) per OWC's instructions with an SSD I had sitting around. I used a 2.5&quot; to 3.5&quot; adapter that would fit the physical needs for the drive upgrade. The drive seems to be seated properly and connected as needed.
After reconnecting wires as instructed, I ran into an issue where the screen is lighting up (the backlight seems to be working fine) and I hear the Apple chime/sound effect, but nothing is displayed. I'm watching the screen and waiting up to 5 minutes, and no icons or UI ever appear.

I tried connecting a separate SATA cable with an external drive, but that made no difference.
I thought that the arrangement of the inverter cables may have mattered, and read people with similar models saying it did matter. However, iFixIt's guide (Step 11, specifically) clarified that the cable arrangement should not matter.

During reassembly, the order of the inverter cables is interchangeable within each socket.

Plus, the clips and &quot;dots&quot; on the inverter plugs line up in a way that there's only one way to orient them properly within the plugs and I tried multiple cable arrangements anyway to see if it changed anything.
I reset the PRAM, but no luck there either. The behavior was the same. A gray screen, the chime, all 4 green debug/diagnostic LEDs on the main logic board were illuminated, but no other visual feedback indicated anything was working.
I connected my macOS 10.11 El Capitan installer USB, which I know works. El Capitan's the most recent version of macOS this hardware will install and the USB device worked fine with the old hard drive. Nothing happens when I boot with the USB device plugged in. I keep manually rebooting, but have no visual feedback for what's happening.
Unfortunately, I have no DisplayPort cable to use with an external display.
What is going on here? Is something broken?
Press the Option (or Alt) ⌥ key on boot. This will allow you to enter the Startup Manager and boot from the USB device.
I do not know why the screen is gray and doesn't simply default to the Startup Manager automatically. That would be a nicer experience since the gray screen that never does anything is obviously a bit confusing.
Whatever the reason for the gray screen, explicitly pressing the Option key before the boot chime works. The display was fine all along. The issue was just that the mac wasn't doing anything by default, and launching the boot manager explicitly then booting from the USB installer works fine as expected.