Unable to boot and tried almost everything I know

[Xtreambar]

My mid-2011 iMac crashed a couple weeks ago and has since been unable to boot up. I've tried a bunch of options, but nothing seems to work

Single user mode to fix the main HD, reset the PRAM, boot from external media, remove all ram and reinsert each with boot-up.

Safe mode doesn't start up. I cannot even hold down C to enable OS re-installation.

All of these paths eventually lead to the Apple logo, a loading bar, and then a gray screen. I am able to run FSCK in single user mode and can select various media from which to boot other than the SSD (recovery partition or SD card with Yosemite installer).

These points lead me to believe there is either a hardware or BIOS-type issue preventing the OS from loading. Should I give up and remove the HDs (HDD & SDD)?

Out of ideas (I had uncatalogued more of them, but the forum post form timed out)

 

[hfg]

I had a similar issue with a 2011 iMac some time ago. I had added a SSD on the 3rd SATA interface and it had been running fine for quite some time. One day, it refused to boot from anything including the optical disk drive. I tried everything I could think of and finally concluded it was probably the logic board ... which I hoped would be covered by Apple Care despite my adding the SSD.

I took it down to my local authorized Apple repair shop and explained the situation and what steps I had taken. The tech called me back later in the day and said it was a bad SSD drive. We were both surprised that a bad drive on one SATA port could affect all the SATA ports. But simply unplugging the SSD allowed everything to boot and run normally. I paid him to put it all back together, removing the SSD of course, and took it home. Once I received a warranty replacement for the SSD, I reinstalled it and everything was again working flawlessly.

Hope this helps...

 

[Xtreambar]

Hmm. That does parallel what's going on. Were you able to recover the data on your SSD by plopping it into an external enclosure?

 

[hfg]

Hmm. That does parallel what's going on. Were you able to recover the data on your SSD by plopping it into an external enclosure?

No ... it either was totally unreadable. I just sent it back for replacement. I did have everything backed up, so I didn't lose anything other than some time.

I don't know if it was somehow jamming the bus, or generating constant I/O activity to overload the bus which caused all other SATA ports to not respond.