If you've forgotten your Windows password, there are several ways to retrieve or reset it:
If your PC is on a domain, your system administrator must reset your password.
If you're using a Microsoft account, you can reset your password online. For more info, go to the Reset your password
If you're using a local account, use your password hint as a reminder.
If you've tried these suggestions and still can't sign in:
If you have Windows 8.1, you'll need to reinstall Windows.
If you have Windows RT 8.1, you'll need to contact your PC manufacturer.