Hello,
Sorry to hear you are having issues. But, need to know more.

1. Your current Windows 10/11 version and OS Build number. Please use Winver.exe to get these numbers.
2. What actually don't work? Any error popup while installing? Has you tried rebooting right after installing finished?
3. What suggested steps have you tried? List them so we don't need to repeat them.

Thank you,
Basj,
Stardock Community Assistant.

Please try Clean boot: Refer here: https://support.stardock.com/space/SHC/1334935592/Start11+Clean+Boot. Do note that Clean boot need to be done with care. Try it and report back.

Thank you,

Basj,
Stardock Community Assistant

Perhaps its a temporary server problem, please try again. If you still having the same result. Try download it from different system.

Thank you,

Basj,
Stardock Community Assistant

In an ideal setup, everything should work seamlessly. However, there’s always the possibility of conflicting software running on a system. That’s why we recommend performing a Clean Boot to help identify which application might be causing the issue.

Alternatively, you can try a Windows Sandbox test to check if Start11 works properly on a vanilla Windows environment. You can find the steps here: https://support.stardock.com/space/SHC/1416855562/Testing+Start+in+Sandbox. 

Regarding the Error 403, we suggest testing the download on another device — for example, your phone or another PC — to confirm whether the issue is specific to your current system.

Thank you,

Basj,
Stardock Community Assistant

Given the symptoms, I would say the software isn't starting up at all other than the config screen.

If you open taskmanager do you see Start11_64.exe and Start11Srv.exe running on the processes tab?

One possibility is you have an AV or antimalware app which is blocking the start of the Start11 service which is listed as Stardock Start11 in the services.msc window.

Yes, I see them both