Are the hands being imported properly into PokerTracker 2? If they are not, you need to resolve that issue first before PAHud can display any hands.
If the hands are importing, instead of using C:\Program Files\Full Tilt Poker\HandHistory\<username> for the directory just use C:\Program Files\Full Tilt Poker\HandHistory\ this should capture all hands played on that computer.
Are you running Windows Vista? If you are, disabling UAC might help, see the following tutorial:
Tutorial: Vista-How to Disable 'User Account Control' (UAC)If none of these helps, please enable logging, play 30 hands on a single table, and attach the log file to a support ticket (play as the user who is having the issues) and we will get your issues resolved. You can find a tutorial on how to create a log file here:
Tutorial: How to Create a Log File