Windows services don't normally interact with the desktop. Indeed, their primary purpose it to run "headless", i.e. with no active user session, and hence no desktop. Why have you chosen to use a service to do this?
1. As others said, Windows services are meant to run in the background.
2. The services which has to run irrespective of the user login, has to be started with a Local System account (the process would have a user name as SYSTEM). It would been, that no user has to login to start the service, once the system is booted, the Windows Service Control Manager will start them.