Installing the demo should have worked fine, assuming you ran the configuration wizard and clicked the "try it now" option (or whatever it is called) when you were asked for a license.
Is this a machine where you installed a SolarWinds demo previously? If so, that an be your problem - SolarWinds places multiple "hooks" into the software to block re-installs. So if you have a scratch server that you use for demoing software, and you've installed SolarWinds on this machine before, you should scrub the OS and then try installing SolarWinds again.
Clik here to view.
