Hi,
Sorry but I must explain what happen to me, it will a bit longer.

1- I created a partition about 80gb on my
C hard disk.
2- Installed Fedora 31 on this partition
But after 10 minutes my screen was
Frozen.
3- Came back on W7, downloaded Ubuntu,
deleted Fedora.iso
4- Ubuntu installer wanted to put Ubuntu
on My A hard disk and partitionate
itself the disk... I authorize.
5- Ubuntu worked very bad too, so came
back on W7, deleted the iso, and I
deleted the partitions one the twice
disk...
6- when I rebooted my computer, I could
read on a black screen:

Error:no such device blablanumberofthedev
Error:unknown filesystem
Entering rescue mode...
Grub rescue >

Please, my computer can't swim, could you
Help it?

Thanks a lot, have a nice day.

Ps: it's a desktop, Windows 7,64 bits, 2.6ghz, 8gb Ram, 2 disks C and A turn at 7200tr/min, and it hope he could run a Gnu/Linux distributions one day will come...

First check this:
https://www.diskpart.com/windows-7/fix-mbr-windows-7-7201.html

1 members found this post helpful.

Sounds like you installed the grub boot loader, then deleted your system, so it has no idea of where to go, & is now asking you.

If you install another Linux system into the partitions that were being used, & install grub again, you should be able to boot into either system. Else, you will need to 'repair' your MS Windows system.

1 members found this post helpful.

when installing Linux and in the disros installer, make sure you find that where to install grub(bootloader) part and make sure it is pointing to the boot drive before clicking install.

if you are reinstalling a system over top of one that is there, make sure you tell the installer to format that partition before installing that current system.

2 members found this post helpful.

I don't get the deleted iso part. Are you booting to an iso or making a dvd?

Burn a dvd of one of these live linux distros maybe and see what you have on your disk. If windows is still intact, make backup or save important data. Use windows maybe to fix boot issue.

I agree that maybe grub is on instead of windows loader.

If you do get windows back and you want to keep it consider a free virtual machine over dual boot maybe.

Linux installers often keep one from installing linux over linux and sometimes puts the new distro on your windows spaces.

1 members found this post helpful.

Thanks a lot for all your purpose, your attempt to help me.
Unfortunately my W7 is dead. So I download W10 and yesterday I installed Linux Mint... Dual boot mode... Amazing. The system looks like run correctly...
Take care and thank you.

You installed a boot loader (together with ubuntu) that caused some issues. Your windows was OK (most probably). But it is now over.
Please mark the thread solved if your problem solved.

[solved]

top right corner, thread tools menu and there you can find it.