Wow, that is very strange. So... SLiMgui launched and worked fine prior to the workshop, but now, at the workshop, it shows a blank black window? Maybe your workshop is cursed??
My best guess is that something else has changed on their machines in the interim that broke things. Maybe Microsoft released a Windows update, and with that update, SLiMgui no longer works? Given that it sounds like this is happening to more than one person, it would need to be a popular/widespread update like that – like a Windows update.
Whatever it is that changed, it is apparently undermining SLiMgui – probably by undermining the Qt framework that SLiMgui uses. It might possibly help to uninstall and reinstall SLiMgui; maybe the reinstalled version will not be undermined in the same way. But it sounds like you tried that.
The other alternative is for these users to use the Windows Subsystem for Linux. SLiM and SLiMgui run fine under that, I think. Then you're basically running the Linux version of SLiM/SLiMgui, not the Windows version. That would probably fix the problem, whatever it is, but it's a somewhat lengthy and complicated process to install the WSL and then install Ubuntu or something inside the WSL, and then install SLiM inside Ubuntu. The manual (chapter 2) has instructions for installing under the WSL. I think they are somewhat out of date; I've been told that they are, but so far nobody has volunteered to update them. I'm not a Windows user, so I really have no idea.
Hmm, I think I have heard people say that if double-click launching SLiMgui doesn't work, launching it via the terminal sometimes helps. I have no idea why that would make a difference, but worth a try?
In the longer term, it would be helpful to get more information from these folks, on a GitHub issue. Version of Windows being used, what hardware they're on, what version of Qt they're using (SLiMgui shows that in the About panel, if it isn't black :-O), what version of SLiM they're trying to run, etc. Maybe the folks that maintain the SLiM installer for Windows will find some information in that that helps them to debug or test what's happening.
Sorry! I hope it isn't biting too many people. Hopefully people can buddy up with non-Windows users and work together?
Cheers,
-B.
Benjamin C. Haller
Messer Lab
Cornell University