Go into services by clicking on start>administrative tools>services. Find the DKservice.exe service and right click on it. Select Stop. Wait for the service to stop and then right click the service again and select start. Now go back and try to start Diskeeper. If that doesn't work, you probably need to re-install the application which shouldn't affect any previous settings you made in Diskeeper but it might so you may have to set up your preferences again.