blank screen after graphic card bios update

[rabbitweed]

i just wanted to boost up game performance so i decided to edit gpu/mem clocks with bios editor on windows 7 that i thought it may help.After the bios update windows seems boot up normally and games works well too but when i tried to boot OSX,screen goes blank now.OSX bootup screen is blank now and tried booting with press & hold ''option'' key trick is not working.white screen with apple logo now showing up.screen is black now and i dont think imac is stucked on booting up OSX
i know windows will boot again but osx bootup is selected,machıine keeps trying boot osx now.any advice?

imac 27'' i7 2.8 with 4850

 

[Ptyger]

Wow. Okay. So you edited the firmware of your 4850 in your i7 iMac to get a little more performance out of games, by installing BIOS code onto the card. Ouch. Macs don't use BIOS code for booting, they use EFI, which is a different implementation altogether.

Basically, from what you've said, it seems as though you overwrote the EFI firmware on your card with whatever updated graphics BIOS you were able to produce. Since Mac OS X doesn't use BIOS, and the drivers in OS X are designed to interact with an EFI based system, you've basically made the video card unresponsive to the OS.

The reason why it boots fine in Windows is because the EFI firmware on the iMac has a BIOS emulator, essentially, that will load when booting into Bootcamp. Thus the 4850, now reprogrammed with BIOS firmware, will be visible and completely useable in Windows ONLY.

In short, you've turned your Mac graphics card into a PC graphics card. I'm not sure if there's any way to restore the Mac firmware to the card in Windows, someone else will have to provide that option as I'm not familiar with the process, and I don't understand it well enough to risk ending up with a brick. Nor do I want to advise you incorrectly as to how this is done.

As much as I'd like to point and laugh, I know how frustrating it can be to do something that would ordinarily make sense and have it turn to poo. I wish you luck, though.