Sometimes you will be asked to completely uninstall pt3 and reinstall it again. These are the steps for doing this.
1) BACKUP YOUR DATABASE
Probably the most important step. Without this, you are back to square one w/your pt3 software and all the data you had collected is up in smoke. Open pPT3, then click on Database -> Database Management, then select your database and click on Export. Select a folder to export to then click OK. PT3 will now Export all the hands from your database to files.
What if you cannot do this? You might be in a situation where you cannot get PT3 and postgresql to talk to each other and then you cannot get to the database to export it. If this is the case, but you still have your processed hand history files stored in the 'processed' folder you can re-import from there. Go to My Computer (computer in Vista) -> c: -> program files -> pokertracker 3, right click on 'Processed' and choose Copy. (Note: if you changed the processed folder on the auto import tab, copy that folder instead). Now go to your desktop, right click -> paste, and this will copy all your processed hands.
EDIT: This will store your hand histories to file, but will not actually back up the database. To store the postgres database, see the end of the Database / Postgres FAQ. Again, this will only work if the postgres service is running. If it isn't - do NOT delete the postgres folders in the following steps, and if you re-install the same major version of postgres (i.e. the same 8.X) and you will be able to reconnect to the existing database after you re-install, on the step where you initialize the database cluster uncheck the box to skip this step.
2) UNINSTALL PT3
Go to Start -> Settings -> Control Panel -> Add/Remove Programs and select both PokerTracker 3.
3) UNINSTALL AND REINSTALL POSTGRESQL
How To Uninstall/Reinstall PostgreSQL 8.3
4) REINSTALL PT3 - Go to here: PT3 downloads. Download the most recent version. DO NOT GET PT3 WITH POSTGRESQL as you already have postgresql installed. No need to install it again. Run the install file and click "I agree" then Install.
5) SETUP PT3'S DATABASE AND IMPORTING YOUR OLDER DATABASE - Run PT3. If you have a registration key, please enter it when prompted and register. Once validated, or when you click on OK, you will see this:
Put dbpass in for the password it is asked for. Your database will be created. Now click on the manual import tab, and click on import from directory. Select the directory you saved your database in step 1. In the case of those of you who could not export your database, but copied your processed folder, select the folder you saved on your desktop. Once your old database has been imported, you can delete the folder that contained your processed/exported database.
EDIT: if you actually backed up the postgres database in step 1, then you will need to restore it as described in the Database / Postgres FAQ.
You should be good to go now with a clean fresh install of pt3.