There are several reasons why this problem may occur:
The target element or monitor is set to not be monitored.
The target monitor's time period doesn't include the current time.
The monitored element isn't properly licensed so all monitors on the target element may stop. An error within the Data Collector has stopped the monitors.
Monitoring station performance may need to be tuned if monitors are running but are well behind schedule or not running in a timely manner.
As a first step, restart the Uptime Infrastructure Monitor Data Collector service to see if this clears the condition. If your monitor continues to not run, please contact IDERA Support and provide a Problem Report and the name of the impacted monitor.
To facilitate a more thorough investigation, also provide the following information: Output of Test Service Instance for one of the impacted monitors.
Screen shot of the Service Status screen for the element hosting this monitor that includes the Last Run Time for the monitor. Include the current monitoring station time when this screen shot was taken.