Hi guys my ssd died on my mac pro 2009 i did firmware upgrade to 5.1 but now for some reason i am not able to install OSX even though i have original DVD that come with my mac. Basically it say this OSX cant be installed on this mac which is 10.6.2 i never head this problem installing and i believe its the firmware issue now i am ruining windows on mac pro how can i roll back to 4.1 is this possible on windows
thanks
Your Mac is now a 5,1. Of course you can't install a OS that only support 4,1 but not 5,1. This is completely normal, in fact, a protection from Apple to avoid install the "wrong" OS which may cause issues (e.g. no proper driver for the newer hardware).
You can't downgrade the firmware in Windows.
There should be a firmware restoration disc for 4,1 (available via Apple web site). But I am not sure if this disc can work in your case.
Besides, You can install the newer OS. Any macOS since Mavericks is free from Apple, just get a friend that using Mac (if you don't have any spare Mac), download the installer for you, and burn a disc. It's also possible to do that via a macOS VM.
Or if you don't know how to durn a disc, don't know how to make a bootable USB. Just take a USB 3.0 HDD to an Apple store. Tell them your situation, ask them to install a macOS onto your HDD. Once you back home, plug that HDD into one of the USB 2.0 port. Then you can boot from it. Once you boot to desktop, you can then download / run the macOS installer, and set your new internal hard drive as the destination. This will also allow you to install the macOS back into your internal drive.
I am not sure why you upgrade the firmware at the beginning. If that's for hardware upgrade (e.g. CPU). DO NOT downgrade your firmware, which will make your Mac unable to boot until you install the old CPU back in.
If you want to use your original factory OS (from your disc). You need to install a macOS first, and then downgrade your Mac back to 4,1 (again, ONLY do this if you NEVER upgrade the CPU). Once you finish the downgrade, you can then boot from the disc and re-install the factory OS back into your Mac. And if you have any other hardware upgrade (e.g. GPU, PCIe USB 3.0 card, etc), go back to factory OS may disable all of them. Your Mac can still boot, but those hardware may not able to work properly due to lack of driver.
