2009 iMac won't boot

[dangerfish]

My iMac has over the past few weeks become unusable and now won't boot to the login screen. It turns on and you can see the Apple logo but the progress bar never advances.
Several years ago, I did a DIY Fusion Drive. The HDD is still in the main position and an SSD is in the optical drive position.
I've tried several of the start up keyboard combinations and nothing works. I created a Sierra thumb drive and tried to boot from that but no joy there either.
Is this likely a hard drive problem, a logic board problem or something else?

TIA

 

[CoastalOR]

It doesn't necessarily sound like a drive problem. If your drive completely failed you would see folder with a question mark (mean a bootable OS is not found) instead of the Apple logo. Now if the drive has not completely failed then you could see a Apple logo but the complete OS load could fail, which is what you see.

But, booting from a bootable Sierra USB installer would take the internal drives out of the equation. Are you sure you have a properly functioning bootable USB installer?

Could you give more details on the "unusable" symptoms, key combinations you tried, and what you saw when trying to boot from the Sierra thumb drive?

 

[nambuccaheadsau]

Sounds like a failed gfx card.

Still nothing with the USB installer plugged in and holding Option after boot?

Then what about Verbose/Safe Mode boot?

The gfx card is replaceable and have a look at this from Apple Discussions:-

https://discussions.apple.com/thread/5197077?start=0&tstart=0

 

[dangerfish]

Could you give more details on the "unusable" symptoms, key combinations you tried, and what you saw when trying to boot from the Sierra thumb drive?

Over the past few weeks, the computer became slower and slower to the point that it just would do anything and I would have to restart it. There were not any visible graphics issues. The computer was just slow and would eventually completely lock up to the point that I couldn't even force quit any of the application forcing me to do a hard power cycle to get the computer working again (for a little bit).

The Sierra installer does work. I tried it in another iMac and it did boot to the installer when holding down the Option key. In the iMac in question, nothing happens when holding down Option. It stays stuck on the Apple screen with a progress bar that doesn't move.

I've tried booting into Safe mode and Single User mode along with Recovery and Internet Recovery. Nothing works. All I see is the Apple screen.

I took the SSD out (leaving on the HDD) and tried rebooting. This time, I saw a circle with a line through it instead of the Apple logo.

I'm using a BT keyboard. I can bring home a wired keyboard today and see if that produces different results when trying different keyboard combinations on boot.

 

[CoastalOR]

I think trying a wired keyboard is an excellent idea. Is a Windows or Mac keyboard? If it is windows, you might want to take a look at this thread: https://forums.macrumors.com/thread...-on-a-non-mac-keyboard.2036007/#post-24376277
Maybe the keyboard will help to boot from the Sierra USB. If that doesn't work then you may be looking at a hardware failure.

Removing the SSD broke your OS since the drives were fused as one logical volume.