Did you install the "Full" version of PT3 which should have installed PostgreSQL for you? Do you see any postgres.exe processes in Task Manager > Processes?
If you still have problems please report your problem so that we can investigate.
i cant connect to my DB either. PT opens normally, but when i either try to auto-import, it fails and says "Fatal Exception during Auto-Import process: Unable to connect to database: PokerTracker 3 Database". I have been using the lagtest version for the past 6 weeks with no problems. i am on Pstars.
For quite a few people recently just restarting their computer will fix this problem. If that doesn't fix it for you, please report your problem as per WhiteRider's link and we'll look into it further for you.