Whatever you installed must have wiped out the registry entries that PT is looking for then.
What version of PostgreSQL have you been running? Open the Start > Settings > Control Panel > Admin Tools > Services window.
Find PostgreSQL in the list, it will say what version it is in the text description (i.e. "PostgreSQL 8.2 database service").
If it's 8.2, then download and reinstall version 8.2
You can get the download file here:
http://wwwmaster.postgresql.org/downloa ... .2.6-2.zipWhen you go to reinstall it, when you get to the window that has "Initialize Database Cluster" at the top left corner - UNCHECK that box and click Next to continue. This will cause it to just try to use the db files that are currently on your computer.