Hi Roy Cone, Shane Miles,
One thing to check would be what service accounts Server and Portal were installed with, and what was used to configure Portal.
If you're not sure this can be checked by opening Services within the Windows Administrative Tools within your start menu. If you're doing a base deployment as a basic proof of concept, it may be worth considering using an account with administrator privileges within the Server and Portal installation.
When configuring Portal, it would be a good idea to ensure that the browser used is run using the same account for the Portal install, and ensure that the account has sufficient privileges to access locations such as the Portal configuration location (default is usually in C:\arcgisportal or similar), as well as the Portal installation directory which contains another configuration file (default is usually <Portal for ArcGIS installation directory>\customizations\<version number>\framework\webapps\arcgis#home\js\arcgisonline\config.js)
When initially configuring Portal, the initial URL provided after the installation completes can be pasted into a different browser instance which is opened using a 'run as' option for the a user which has appropriate permissions as above.
It may be necessary to uninstall the Portal Web adaptor, Portal installation and delete the above directories and try again.
If this has been helpful or answered you question, please mark the response to help other GeoNet users!