You should have 2 files setupact.log and setuperr.log. Probably in C:\Windows but perhaps in C:\Windows\Panther.
See if you can find some created today when you ran the command. You can open them in Notepad or something. Mine just says this in the activity one and the error one is empty...
With a bit of luck yours will say what it thinks it has a problem with.
2016-01-08 13:47:39, Info UI Determining whether we should run ConX or legacy setup
2016-01-08 13:47:39, Info UI Will launch ConX setup experience
2016-01-08 13:47:39, Info UI Launching ConX setup experience
2016-01-08 13:47:39, Info UI Launching E:\x64\Sources\SetupPrep.exe /Auto Upgrade /Quiet /NoReboot /DynamicUpdate Disable /Compat ScanOnly
Feel free to upload them if you like (I don't think they contain anything personal but you might want to check)