Welcome to Microsoft Q&A forumI’m sorry you’re dealing with this. Seeing an old account name does not necessarily mean someone has stolen your credentials. The Windows PIN belongs to a particular user profile on that computer and is different from your Microsoft account password.
Please try these simple checks:
- Restart the laptop.
- On the sign-in screen, look in the lower-left corner for your usual account. If it is not shown, select Other user, if available, and enter the email address and password for the correct account.
- Once signed in, open Start > Settings > Accounts > Your info. Tell us the account name shown there and whether it says Administrator or Standard user. Do not post your email address.
- If you cannot use the correct password, try Sign-in options > I forgot my PIN.
Please do not delete accounts, reinstall Windows, or remove files yet. Also, please note that this is a public support forum, so we cannot access the laptop, change its administrator, or forward the case internally.
Hope this helps, please feel free to let me know if you need any further assistance