Hi Lando, I haven't heard of any issues on Windows 8.1 launching ad hoc analysis, this is usually caused by the browser not starting Java. Here is something your user can try to narrow the issue:
1. Right-click the Launch Ad Hoc Analysis button, and save the link. This will be a file called discover.jnlp.
2. From a command prompt, run: javaws c:\path-to-file\discover.jnlp
That should launch the app. You could also try launching some of the demo jnlp files on the Java site, here are a few: http://docs.oracle.com/javase/tutorial/deployment/webstart/examplesIndex.html