With PT closed, go to the Start > Settings > Control Panel > Administrative Tools > Data Sources (ODBC) window. Click the System DSN tab. Find PTRACKHH in the list and click on it then click the Configure button. On the next window click Repair and then OK when prompted.
When was the last time you backed up your database files? If you haven't then go to the c:\program files\poker tracker v2 folder. Is there a file called hhcopy.mdb there? If so, rename the current hhdb.mdb file to hhdb_bad.mdb and then rename the hhcopy.mdb file to hhdb.mdb