Use your Microsoft account password instead of the PIN
On the Windows sign-in screen:
Click "Sign-in options"
Choose the key/password icon
Sign in with your new Microsoft account email + password
Once you're in, you can go to Settings → Accounts → Sign-in options and reset the PIN from inside Windows.
If you have forgotten the password:
Go to account.live.com/password/reset on another device and reset your Microsoft account password using your new email. Then come back and use steps above.