Howdy scad_mfa,
Welcome to Apple Support Communities.
It sounds like you’re running into issues sending and receiving iMessages on your notebook after changing the password for your iCloud account. The article linked below will walk you through the process of updating the Apple ID information used by Messages and other Apple services on your devices.
What to do after you change your Apple ID email address or password - Apple Support
Mac with OS X Mountain Lion or later
Open the Messages app, select Messages > Preferences, then click the Accounts icon.
- If you're signed out, click Accounts and sign in with your updated Apple ID or password.
- If you're signed in with your previous Apple ID, click Accounts, then select your Apple ID from the list of accounts. Click Sign Out, then click Sign Out again when asked to confirm. Sign in with your updated Apple ID or password.
Take care,
-Jason