Here some tips if you having this problem:
* Check your Account you used: username and password if correct or mismatch (Be sure if you're username or password is correct)
* Check your Internet Connection or maybe the Server have problem or down
note: Reset your modem
* Try to Open in another Computer or Laptop if problem persist you should sign up a new account in Messenger (but you lost all your contacts)
* Uninstall Messenger and restart your Computer or Laptop, then Install Messenger again a latest or newer version.
* Update your Anti-virus or any program you used to protect your Windows, It's a kinda a spyware or virus infected sometimes.
* One tips be careful to open some untrusted site's..because it harm your Computer or Laptop.