Were you able to login to your organization from the web browser using the same machine? On the blank area Dashboard is actually trying to show the login page, and the page itself is defined by your org admin, so trying to sign in from somewhere other than Dashboard will be a good test.
There are a few more pieces of information that would be helpful for us to understand the issue better: - Using Fiddler or other web debugging tools, did you see any 4xx errors when the Dashboard was loading up the blank page? - Did you download your Dashboard from ArcGIS Online (http://www.arcgis.com/opsdashboard/OperationsDashboard.application), or from your Portal for ArcGIS? - How is your portal secured? Is it by token, network credential or PKI?