Hello, Unkown Vazguz.
Welcome to Microsoft Community.
From your description, I understand that you reinstalled Windows, but an error occurred.
I noticed that you have backed up your data. Did you back up your data to an external hard drive?
If not, please back up your data to an external hard drive or other safe place.
This may be caused by an exception during the Windows installation process, which then destroyed the boot partition.
Please try to reinstall Windows again.
(Clean installation, when selecting the installation disk, delete all partitions, then create a new partition, and then install.)
Disclaimer: I recommend that we try to perform a clean install to get your computer back into a working condition. Please ensure that you backup any important data, including Documents, Pictures, Videos, and more.
Once you are done backing up, you can follow the steps in the following guides:
How to: Perform a Custom Installation of Windows 11 and Windows 10 or - Microsoft Community
If the problem still occurs, please try to recreate a new USB boot media first.
If there are any updates, please feel free to reply.
Best regards.
Malygos.Z | Microsoft Community Support Specialist