In the Operations Manager console of Microsoft System Center Operations Manager 2007, the Windows Operating System column may have a Not Monitored state for a new agent. Additionally, the state never changes to Healthy.
This issue occurs because the new agent has the same NetBIOS name as a previously installed agent. When the agent is deleted from Operations Manager, the grooming of the deleted agent is hard coded to occur after two days. Therefore, the agent is not immediately groomed out of the database completely.
We document this issue and the workaround in the new Knowledge Base article below:
KB979387 - The "Windows Operating System" column has a "Not monitored" state for a new agent
J.C. Hornbeck | System Center Knowledge Engineer