Two days ago I try to make a dual boot (I have BIOS Legacy) installing Ubuntu 21.04 in addition to Windows 10.
Initially I think all was ok, I formatted an USB and converted it in a flash memory with Ubuntu ISO using Rufus. Also I made a partition giving 40GB of free space in Disk1 where I have 1TB (of D: disk).
As I was following a tutorial to do this, the part of reboot my PC and enter to the Boot Menu in the BIOS is the part that isn't as lineal as the rest of the process.
So I couldn't follow the tutorial in that part, then I searched another explanation (and I think that was my error) I disabled both FAST BOOT and CSM SUPPORT in my ASUS BIOS, I understood that doing that was necessary to reach the Boot menu and avoid Windows initiating automatically, so I saved the changes and got out of the BIOS.
In that moment I got a black screen. I waited for a while and then reboot my PC. Since that point the manufacturer logo haven't appeared again. After a few seconds, the first thing I saw in screen was Ubuntu logo loading, and then got into the Installation Menu.
When I reached the part of selecting to make the installation alongside Windows 10, erasing disk or personalize it, I only have the last two options, so Windows wasn't being recognized.
At first I cancelled the instalation and checked in file manager that all Windows 10 data fortunately wasn't lost, but when I look for the names of the partitions, it was only mentioned NTFS but in nowhere Windows 10.
I tried to use Boot Repair, but when I execute 'sudo apt-get install boot-repair' I got something like 'E: Cannot find package boot-repair'. So I thought that could be happening bc I am 'using' Linux without installing it. So I made a personalized installation, using the free space, and also setting a swap partition and an EFI one.
Fortunately, I didn't lose data, but I still couldn't install boot-repair, same error. I also install the Boot Repair ISO and load it into a formatted pen, I updated grub, modify some file, but I can't get to the BIOS or to anywhere at all since I made that changes that leave me on Ubuntu, any button I press on reboot never take me to anywhere else than the login screen...
I don't lose data but I don't know what to do, or how can I revert what I did, the recommended things aren't working for me, the manufacturer logo disappeared so I never see that text on screen 'F2 to setup BIOS' again, it's going directly to UBUNTU after a seconds of black screen. It's a little desesperating and frustrating situation, lets see if someone has an idea of what else can I do or what is exactly the problem.
I am a Linux beginner, sorry for the ignorance. Thanks!