On Windows 11 BitLocker drive encryption can often be enabled automatically without you even being aware it has happened.
If your computer crashes or has problems stating then you may see a screen similar to below asking for your BitLocker recovery key.
To retrieve your BitLocker recovery key you will need to login to your Microsoft Account from another device e.g. another computer or a phone / tablet (if you don't have any other devices then contact me and I will do it for you)
To do this:
1) Click the link below:
https://account.microsoft.com/devices/recoverykey
2) Sign in with your Microsoft Account credentials
3) Once logged in click Devices down the left and side
4) You will see a list of your computers, click the arrow at the end to expand them and find the one which matches the ID shown in your BitLocker recovery message (as per example highlighted in red above)
5) Click View Bitlocker Keys and here you will see the long code you need to enter in the box
N.B. If you don't have a Microsoft Account then when you encrypted the drives on the computer you would have been provided with a BitLocker recovery key and been asked to save it or print it out, if you don't have this then repair will not easily be possible and the computer would have to be wiped and reinstalled from scratch, potentially losing any data on it unless you a) have a backup or b) your data is synced with OneDrive (or similar)