I had ArcGIS v10.2 for Desktop installed on a PC and the licence needed to be updated. I made the mistake of uninstalling v10.2 re-booting and installing v10.5.1. I obtained a new provisioning file from my employer and licenced ArcGIS as normal. ArcGIS said this had been successful. However, when I tried to run the software I got a 'not authorized for use' error. I then uninstalled everything once again and manually removed additional items following these instructions: http://joelmccune.com/completely-uninstall-arcgis-for-desktop/
After reinstalling ArcGIS 10.5.1 I got the same error. I have tried de-authorizing ArcGIS but this didn't work.
I don't know what else to do. I think I'd like to put my PC back to a time before ArcGIS was installed and start from scratch but don't how to do this as the Esri no longer provide a utility for this purpose.
It's all a bit of a mess. Can anyone help?