Jenkins tries running a job on the Master node, and in so doing tries installing a JDK:
Installing C:\Program Files\Jenkins\tools\hudson.model.JDK\JDK_auto-install_\jdk.exe
[JDK_auto-install_] $ "C:\Program Files\Jenkins\tools\hudson.model.JDK\JDK_auto-install_\jdk.exe" /s /v /qn /L '"C:\Program Files\Jenkins\tools\hudson.model.JDK\JDK_auto-install_\jdk.exe.install.log"' REBOOT=ReallySuppress 'INSTALLDIR="C:\Program Files\Jenkins\tools\hudson.model.JDK\JDK_auto-install_"'
This hangs indefinitely (100% reproducible). I'm guessing this has to do with the fact that Jenkins is running under a non-interactive SYSTEM profile.