If the monitor is failing due to login, then obviously the monitor is not going to work. I've set up WMI monitors on F5 before to monitor a particular service, and start it up on a second box if the service is not running on the primary.
To troubleshoot WMI, try executing wmic from the command line (assuming that you're using wmic to run a query), it will tell you why it can't log in to the Windows system. Usually it's something simple such as using a domain account and not escaping the backslash. But if wmic can't log in, then everything else is useless until that gets fixed.
Try something like
wmic -U Administrator% // "select * from win32_process"
If your credentials are correct, that will definitely return sometimg