This video shows the resolution for a common error message : "Error - Dashboard running user is inactive" and shows the click-path to change the running user to a different user.
In addition to an Inactive User causing an issue with Dashboards, the Running User also dictates what data is queried and displayed in the Report/Dashboard.
If your company has Market Segments and Sharing Rules to only share each Market Segments data with the Users in that specific Market, you will want to be sure the Running User of the Dashboard is a User in the same Market Segment (check their Role, and your system's Sharing Rules).
Be sure to also check the User's Profile for the Running User of the Dashboard. If you only want data for a specific Market to be displayed in the Dashboard, the Running User's Profile cannot have View All or Modify All permissions for the objects in the Report/Dashboard.