Was the postmaster.pid file in your C:\postgreSQL\data folder? If it is delete it, reboot and try starting PokerTracker 4 again. If not then click your Windows Start button then type the following command:
services.msc
and click on it when it appears. Do you see the PostgreSQL service in the list? Is it started, or can you start it? If the PostgreSQL service is listed but not starting then open the Event Viewer (in the same way - if you type 'event' you should see it). In the top left section, expand "Windows Logs" and click on "Application". Do you see any recent errors in the top center section for PostgreSQL? If you do let us know what they say. I had also already recommended that you upgrade from PostgreSQL v8.4 but ideally you would want to reconnect to PostgreSQL v8.4 so you can backup your poker data before upgrading.