You don't need to do anything to activate the HUD. Once Auto Import is running and you have a table open with hands being imported, the HUD will be shown once a complete hand has been played.
If the HUD is not appearing please try these steps:
These filters can interact with each other in ways which may not be immediately obvious, but setting them as described above should remove any of these issues.
As an example if you have the Minimum Hands set to non-zero and Player Ranges enabled then this could prevent any stats being shown when there are more or less players active then the tables you normally play.
If you still can't get the HUD to appear please report your problem so that we can check your configuration and troubleshoot the issue.
The best thing is to enable logging and restart then play about 20 or 30 hands at a single table.
Take a screenshot of the table and attach it along with the hand history file for the session and the PokerTracker.log and PokerTrackerHUD.log files to a Support ticket.
If the HUD is working but has partial stats or is slow or "laggy", or the stats disappear from time to time try some performance tweaking:
8.4.x is supported too and you should generally keep that updated too although we don't have any specific known problems with older 8.4 versions.
Although 9.0 isn't officially supported yet we do have several people using it with no reported problems (including at least a couple of the PT team).
Before you do this you should stop the PostgreSQL service so that your database files can be defragged too (Start > Programs > PostgreSQL > Stop Service).
You can see the state of the cache in the Status Bar at the bottom of PT3. If any of the values are not 100% then you should run Housekeeping immediately, from the Database menu.
Once your database's cache is at 100% (optimum) it will be kept updated automatically during Auto Imports, but if you do any manual imports or add any custom statistics then you need to trigger the cache update manually via Database > Housekeeping.
You an either Update Cache or Rebuild Cache.
If you choose Update Cache PT3 may Rebuild instead if it is estimated to be faster, but if you choose Rebuild Cache that will force a complete rebuild of the cache from scratch, which is good for making sure everything is correct if you're seeing strange behaviour.
Which of these you should choose depends on how big the import was - as a general rule if you import less than 10% of the number of hands already in your database (e.g. less than 100k hands into a database of 1M hands) then Update Cache will be fastest, but for more than that Rebuild Cache will be faster.
If you still have issues please report your problem so that we can check your configuration and troubleshoot your specific issue.
If you have problems with Preferred Seating or Auto Center, or even stats appearing by the wrong players when you are not using these options please read the Preferred Seating tutorial. The "Troubleshooting" section in particular should help you get things sorted out properly.