Stuck during clean install on a new SSD on a late 2009 iMac
I would say you need to take your machine in for repair. You have detached all external devices that you can: with possible exception of mouse&amp;keyboard?

Reset machine
Sometimes if volumes don't appear in Startup Manager (what you get when you hold down the Option key at startup), you need to reset the Mac's PRAM, NVRAM. Shut down the Mac, then power it up, and before the screen lights up, quickly hold down the Command, Option, P, and R keys,( I hold down the keys before pressing the power on button, but requires some contortion. )  until the Mac has chimed twice more after the powerup chime. 

Andy Betts  lists machine specific variants for this procedure in this article:

https://www.makeuseof.com/tag/reset-macs-smc-pram/