You should check the integrity of your installed .NET Framework version, and should ensure that v4.5 or higher is installed.
Did this and that but couldn't get the crap (.Net, not your GUI) working again.
Fixed it by reinstalling Windows 8.1. Thanks for your suggestions, though.

Internet is full of reports of users not being able to fix broken .Net runtime. For such reasons I'd rather like to see a compiled qt GUI. Qt usually doesn't have the tendency to randomly destroy itself without any identifiable reason.