Hello, andreabassetti
Welcome to the Microsoft community.
Thank you for your feedback. If you need to log in to the computer but you have forgotten the password for the account, the only way you can try at the moment is to reinstall windows. you can refer to the following link:
How to: Perform a Custom Installation of Windows 11 and Windows 10 - Microsoft Community
For file backup, you can refer to the following link:
Rescue Files when Windows Won't Start - Microsoft Community
If you need to recover the account so that you can log in to Windows, you can try to fill out the account recovery form.
Help with the Microsoft account recovery form - Microsoft Support
If that doesn't work, you can contact online Chat support. Describe your problem specifically.
Contact Chat:
Go to the following Web site: Contact - Microsoft Support.
Enter your account and click on Get Help.
Click on contact support.
Select windows, account login.
Select Chat with support in your browser.
I look forward to your feedback.
Best Regards,
Aaron| Microsoft Community Support Specialist