Flashing ? at boot on 2011 MBP. I'm really stumped on this one...

[Tony Danger]

So I'm trying to revive a 2011 MBP 13" with the flashing ? at boot but I'm just stumped:

I have tried the followinf:

1. Changed the HDD to an SSD.
2. Changed the RAM to known good ram.
3. Replaced the HDD cable inside the system.
4. Installed various Mac OS & Linux OS
5. When I pull the internal drive out and connect it via USB, I can boot from it over usb fine.

I just cannot boot from it when it's hooked up internally. Nothing seems to work. It always just comes back to the flashing ?

• When I hold option at boot, the SSD can be seen. When I select it, flashing ?
• When I boot from a drive plugged in via USB, the OS can see the internal drive. It can read and write to it, but it just cannot boot.

I have no idea what to do next. Any suggestions? Thanks.

 

[Juicy Box]

It could be a firmware issue.

Did you have this issue with the HDD? Or did it start after you swap the HDD for an SSD?