Hi rohomes and thanks for your post.
Can you check if AltTabby64.exe (assuming 64 bit) is running on your PC?
It may be something is stopping the process from launching.
End of Neil's quote
To check, in Task Manager you should see some AltTabby processes running.
Also, if the install was successful, the configuration app can be launched (AltTabby from the Start menu). This effects the way AltTabby appears/behaves (and can be used to disable it).
If you're not able to open that, or the process isn't running, perhaps try installing AltTabby again.
If there's any errors when you install or launch the app, please let us know what they say.
It may also be helpful to know what configuration/style settings you have selected. If you continue to experience any trouble, a screenshot image of your settings can be included in your reply and may be helpful.
Best regards,
Adam McGuinness
Stardock Support Specialist