MP 1,1-5,1 Black screen after trying to boot into OS 10.11

[Flocarino]

For some stupid reason I chosen os 10.11 as start up disk in my preferences and after the cMP boots, I have only a black screen NO VIDEO, wish I would have let it in 10.14.6 and didn’t try that boot prefrernce.
Now I don’t know how to get back to the ssd with MOJAVE on it. I have tried holding Option key on start up to no avail......The card is a Sapphire Pulse RX580.
Am I missing something here!?
Any help how to get back to Mojave ssd will be highly appreciated.
Thank you in advance

 

[bsbeamer]

Easiest solution: remove all drives EXCEPT the Mojave SSD. If that is not possible, try your original EFI GPU.

 

[Flocarino]

Thanks BSBEAMER, I was doing exactly that when I saw your reply here.....just finished removing all the spinners with OS 10.11 and leaving just the SSD’s installed...to force a Mojave start up.....and IT WORKED....finished putting all back together and all is as before..lesson learned the hard way here.....just to say that first I installed the original ATI 5770 simply to realize after securing the card in place with the bracket, that I don’t have any apple mini display or DVI to Display Port adapter for the new screen....then realized that my last solution, is to pull all the spinners out....
Thank you once again

 

[fhturner]

You might also try holding down Command-R during startup to boot the the Recovery partition. Not sure, though, if you had a 10.11 Recovery partition on that drive and a 10.14 Recovery partition on the other, how it would choose. So that may not have gotten you anywhere, but would've been worth a try.

 

[crjackson2134]

You might also try holding down Command-R during startup to boot the the Recovery partition. Not sure, though, if you had a 10.11 Recovery partition on that drive and a 10.14 Recovery partition on the other, how it would choose. So that may not have gotten you anywhere, but would've been worth a try.

It chooses the recovery partition of the last selected boot disk.

 

[Flocarino]

You might also try holding down Command-R during startup to boot the the Recovery partition. Not sure, though, if you had a 10.11 Recovery partition on that drive and a 10.14 Recovery partition on the other, how it would choose. So that may not have gotten you anywhere, but would've been worth a try.

Sorry, but none of the possibly key combination worked, tried them all, before unplugging the drives.
Thanks