Hi!
What solutions have you already tried to avoid duplicate solutions?
If BitLocker was enabled, something happened. If you haven't replaced any parts on your laptop, either a BIOS update was performed (Lenovo laptops usually have quite a few BIOS updates installed by Windows Update), or your BIOS may have been reset for some reason.
Either of these two options activates BitLocker and may also lock your PIN for security.
If you can already access Windows using your password, you can log out and log back into your Windows account. Have you done this?
- This may solve your problem. But if your computer has been locked, you won't be able to log in and will need to restore it.