imac 27 2011 no boot screen after trying to replace gpu

[Mozambik]

Hello everyone,

I have the following problem with my iMac 27 2011 Intel Core i7 3,4 GHz. (High Sierra). After an unsuccessful attempt to replace the graphics card with the Quadro K3100M I went back to the factory AMD Radeon HD 6970M 1 GB. Unfortunately, I lost my boot screen and boot menu. The key combinations that are used when starting the computer do not work.

 

[Nguyen Duc Hieu]

Hello everyone,

I have the following problem with my iMac 27 2011 Intel Core i7 3,4 GHz. (High Sierra). After an unsuccessful attempt to replace the graphics card with the Quadro K3100M I went back to the factory AMD Radeon HD 6970M 1 GB. Unfortunately, I lost my boot screen and boot menu. The key combinations that are used when starting the computer do not work.

So you can boot to the desktop as before, correct?
Then do a SMC reset plus PRAM reset to see if it helps.
What went wrong with the K3100m?

 

[Mozambik]

So you can boot to the desktop as before, correct?
Then do a SMC reset plus PRAM reset to see if it helps.
What went wrong with the K3100m?

correct but after startup you can see a white screen. Apple logo and status bar are not displayed. Then a card appears asking you to enter your password.

How do I reset the PRAM if the key combination does not work when I turn on the computer. I can't run Apple hardware test, safe mode or startup manager.

 

[Nguyen Duc Hieu]

correct but after startup you can see a white screen. Apple logo and status bar are not displayed. Then a card appears asking you to enter your password.

How do I reset the PRAM if the key combination does not work when I turn on the computer. I can't run Apple hardware test, safe mode or startup manager.

The reason: I doubt that the PRAM got messed-up when you changed the GPU. reseting PRAM may turn it back to previous status.
Key combination won't work if the bluetooth device driver is not loaded first.

First do an SMC reset. (simply unplug the power cable, then plug it back after 10 seconds)
Boot the machine on to see if anything changed.
Then turn off the machine and remove the SSD.
Power the machine on without the SSD to see whether the folder/question mark screen show up.
Now hook-up a wired keyboard to the USB port, if you have been using bluetooth keyboard so far.
Try doing PRAM reset on the USB keyboard.
If you are using a mechanical keyboard like me, then you will not be able to do PRAM reset, etc. Those keyboards are not recognized by the iMac quickly enough for the tasks.