Have you updated any anti virus software or firewall?
Are you using Vista?
Are you running PT3 as Administrator? Right click the shortcut and select 'Run As Administrator'. This is different to being logged in as an Administrator.
Otherwise, Please see the instructions in '
enable logging' for how do do this when you can't start PT3, and submit your PokerTracker.log file to the
Support system , and link to this thread in the reference field of the ticket so that we can investigate.