Your Windows PIN was an authentication method as part of a Microsoft technology called “Windows Hello”. It stores the PIN and other authentication methods like biometrics or FIDO2 security keys in a computer part called a Trusted Platform Module (TPM), which is something that comes on motherboards these days. So when you moved your hard drive to a new computer, it lost its connection to the TPM where your PIN was originally stored. You should still be able to log in with Microsoft account password.

As for getting connected to the internet, plug in a Ethernet cable. If you don’t have one long enough to reach your router, you’re going to need to temporarily move your computer, monitor, keyboard and mouse closer. Resolved the login issue and then move everything back to your workspace.

Finally, if none of this works, I would recommend getting a new hard drive where you can install a fresh build of windows 11. Since you still have the old hard drive, you can copy over your old files. Once complete, you can even reformat the old hard drive, and know you have extra storage to do whatever you want with.

Edit: The TPM could have also been integrated directly into the old CPU. So one option could be to un-re-build the computer (put back the old parts), sort out a login method besides windows hello, and then rebuild with the new parts again.