Hello again
Thanks for your (both you and Leesureone ) reply and your help, I booted the system with the USB installer now i can boot the system.
But unfortunately, my boot sequence have a problem that I can't manage to handle. Please help me to manage it, it seems rocket science for me.
Now I have 2 separate SSD's.
One has High Sierra installed ( the old one). And the new one which has Catalina on it.
And I have 2 scenarios:
1. When I connect my old High Sierra SSD and boot system.
-If I untouched keyboard (press F12) it boots to "Realtek pci etc.."
-If i press f12 and select 2nd entry on the menu it boots to High Sierra . Other entries take me to "Realtek pci.." screen.
View attachment 528762
also my bios entry screens are as follows:
View attachment 528763
View attachment 528764
2.
When I connect my new Catalina SSD and boot system
-If I untouched (press F12) it boots to realtek pci etc..
-If i press f12 and select 6th or 7th entry option it boots to Catalina. Other entries take me to Realtek pci screen.
View attachment 528765
And When i connect my new Catalina SSD here is my bios boot menu:
View attachment 528766
View attachment 528767
I know maybe I attached a lot of information, but I'm desperately needing help and don't know the technical terms to express my problem.
Now I’m wondering how to manage this problem I am afraid to take action to make changes in bios boot menu, to turn things more catastrophic.
I want to use my new Catalina without interrupting to boot menu also I want to be able to use High Sierra installation if there will be some sort of need some time.
My kids and I use this pc all the time we have separate 3X1TB HDD to save our documents stuff. Its important for us to make this pc work again.
Thank you for your time again I really really appreciate all your help and effort.
I am desperately waiting for your ideas.
Thank you all again.