Are you able to open the NoteCaddy application from the PT4 menu PokerTracker+ > NoteCaddy > Show NoteCaddy?
Task Manager is a Windows application that allows you to see all running processes.
Click Start in Windows and type 'task' and run Task Manager. Depending on the version of Windows you have you may need to expand 'More Details' to see the Background Processes section to find "NoteCaddyPT4".