Same happened to me, it stopped working after some Windows update. I have uninstalled it and tried to reinstall, now I'm getting the error message "Installer user interface mode not supported".
This definitely happened following the most recent Win 10 updates. Both my laptop and desktop are showing the same symptoms. I keep receiving prompts to run support assist, but then it just opens a screen and shows not responding in the header. To my knowledge the Win 10 update is the only thing that changed on both computers.
Could you please provide me some of details :
Which type of SupportAssist ? : (Enterprise, Plugin OME, Client)
which version do you have? : (version 1.1 or 1.2.1)
Could you provide me KB Microsoft installed with Windows Update ?
I'm having the same issues as noted above occurring on my XPS 7760 AIO 27 running Windows 10. In my case I am running Support Assist Version 220.127.116.11 and the last two Windows Updates that were applied are KB4284835 and KB4287903. These were applied about the same time so I'm not sure which affected SupportAssist but am assuming it is KB4284835 since that was a cumulative update for Windows 10 while the other update was a security update for Adobe Flash Player.
I also discovered that Dell Help & Support (version 18.104.22.168) also no longer works. While this application loads (unlike SupportAssist), it does generate continual messages that it is unable to connect to Dell Support. The message text reads: "After a few attempts, Dell Help & Support failed to connect to the service. Do you want to quit?"