Start8 automatically starts when your machine starts and there is no option in the UI to disable this (Lightstar is thinking of the feature to go to the desktop)
As Roloccolor has suggested it sounds like something went wrong during install. Start8 uses a service to startup and by the sounds of it something stopped this from being installed. Do you have any antivirus / anti malware software which was trying to be helpful?
I would recommend uninstalling Start8, rebooting, disabling any anything that might interfere with installation, installing Start8 and then turning back on anything you turned off. Hopefully that will sort it.
As an alternative the service can be installed from an admin command prompt by running Start8Srv -install from the command prompt.
