How do I unlock my hard drive locked by bitlocker?

If the password that you used is not valid when booting it as a secondary disk, you may need to find your recovery key.

This is different than a password. It is a randomized string of 48 characters organized as such:
A1B2C3-D4E5F6-G7H8I9-J0K1L2-M3N4O5-P6Q7R8-S9T0U1-V2W3X4

If you do not have your recovery key documented anywhere, you can find it by logging into the Microsoft account associated with that recovery key, verifying your identity, and then recovering it there. See those steps here: https://support.microsoft.com/en-us/wind...

Depending on a number of factors, you may or may not be able to unlock this drive when using it as an external drive. If you are never able to access the "insert your recovery key" screen, you may need to use it as a boot drive. Your computer will have an option during bootup, typically something like pressing Esc, F2, F8, F12, Del, etc. Mash that button during boot up and you'll be taken to your BIOS screen, where you can change your boot priority to favor the external. So long as that drive was not the cause of your old computer crashing, you should be able to boot from it even as an external drive, letting you get in and remove the bitlocker encryption so that you can safely remove all of your data.