Help with 2009 Mac Pro not booting from El Cap USB after an update failure

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...