Is PokerTracker4.exe showing in Task Manager?
It could be off-screen if you disconnected a second monitor as pt4pt4pt4 suggests - in that case set it to be active in Task Manager and press alt-space then use the cursor keys to move it back onto the main screen.
Otherwise, please let it run for 15 minutes or so and then attach the PokerTracker4.log file (from the folder C:\Users\yourname\AppData\Local\PokerTracker 4\) to a
Support Ticket so that we can see what is going on.