Mac Pro not booting after update Mac pro 2009 4,1 Boots up but no video output (black screen).
It was working fine on the old OS that was on it(not sure which OS). I want to update to the highest OS (el capitan) it can run. So I did. But after that I get an black screen.
I tried to reset some things like time code, vram etc. Nothing works. Can't even go to the BIOS to reset everything (or I've got the wrong key combination).
I have also added two other hdds. And on one of them was an Windows installation. So I hold the option key on startup to choose an other hdd and choose the Windows one. And that was just working fine.
What can I do to run Mac OS again? Also tried an Bootable USB with el Capitan but It won't recon the USB flash drive I've made on my 2019 Macbook pro.
When I use Option + Command + P + R
And waited till the second time hearing the startup sound it looks like it's working fine.
But still no output. I see the Apple logo in the beginning but after that no output.
De Mac pro itselfs keeps running with no errors or blinking lights.
Gpu is an ATI Radeon HD 4870 512MB Mac Pro Graphics Card
6gb ddr3 ram
And de standard Xeon 2,66 MHz cpu
Ive downloaded El Capitan, (it's in the downloads folder, DMG FILE).
Then I go to the terminal and I fill in:
sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/THENAMEOFMYFLASHDRIVE --applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app

Fill in my password next, and than it says:
'
sudo: /Applications/Install OS X El Capitan.app/Contents/Resources/createinstallmedia: command not found.
Catalina can't put it in de application folder for some wierd reason...
Adventures In Imaging El Capitan Bootable Media
According to this macOS KB Article (https://support.apple.com/en-us/HT201372)

&quot;El Capitan downloads as a disk image. On a Mac that is compatible
with El Capitan, open the disk image and run the installer within,
named InstallMacOSX.pkg. It installs an app named Install OS X El
Capitan into your Applications folder. You will create the bootable
installer from this app, not from the disk image or .pkg installer.&quot;

I just attempted creating a bootable  on Catalina and when running the PKG it says it will not install on this Mac as it is not compatible.
So I attempted to work around that problem. I had to use CharlesSoft's Pacifist utility which allows the extraction of any type of Mac Package file format. Since I am a MacSysAdmin I have this utility already and it comes in handy all the time.  Unfortunately, it's not open source and it's not free. But for $20 shareware it does what it says it does and it does it very well.
I was able to extract the PKG from the DMG:
InstallMacOSX Folder
  └──InstallMacOSX Folder
       └──Install OS X El Capitan

Then I moved &quot;Install OS X El Capitan&quot; to &quot;/Applications/Install OS X El Capitan&quot; and then I ran the El Capitan &quot;createinstallmedia&quot; command.
sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app


Guess What? That Does Not Work!
I even tried using DiskMakerX ver 6 and ver 9 and it didn't work either. Stated my El Capitan was an incomplete download which it is not an incomplete download.
So back to the drawing board. I try it on Mojave instead. My Mac is dual boot Mojave / Catalina. So in Mojave, it still doesn't work.
Copy it over to the High Sierra Mac.  Finally, some success. The DMG PKG file installed in /Applications/Install OS X El Capitan and I was able to burn a flash drive.
It Only Works on macOS High Sierra or older
So your options are to find someone with a High Sierra Mac or maybe you could install VirtualBox (free), Parallels, VMware Fusion and install High Sierra as a virtual machine then use that to burn an installer. FYI, it can be tricky to access a physical USB in a virtual machine.
Once you get it working, hang onto that working boot USB drive since it's such a terrific pain to build one!  The way the El Capitan createinstallmedia works, varies considerably from the newer macOS versions. It doesn't have the normal InstallESD.dmg, etc.