You may have trouble connecting it with the connector since you installed the forum in a subdomain. The connector will try to include some of the phpBB files... and it may have trouble accessing them in a subdirectory.
When you install phpbb it asks for the database to be installed in... This is also located in the config.php file in the forum directory... compare that with where you installed Joomla... can find it from the admin side System -> System Info or in Joomla's
configuration.php file
Joomla
$mosConfig_host = 'localhost'; // This is normally set to localhost
$mosConfig_user = ''; // MySQL username
$mosConfig_password = ''; // MySQL password
$mosConfig_db = ''; // MySQL database name
$mosConfig_dbprefix = 'jos_'; // Do not change unless you need to!
Easiest way to put them in the same database if they are not there is to reinstall phpBB into the Joomla database... otherwise you need to move all of the tables and hand modify the config.php file to match... and hope there is not something else needing updated...
Then if your phpBB has already been in use and you want to move the posts then copy the tables over the newly installed ones in the Joomla database...
One thing. Everything was working fine, but now when i click on the plugincp I get a "file not found "index.php". Thinking I may have deleted it mistically, I reinstalled the plugin. No "index.php".
Check which directory it is reporting that for... phpBB Connector does not have an index.php... so it is either the index.php for Joomla or phpBB... neither should be missing or you will see big problems...
My guess is that is has to do with the forum in your subdomain. When the connector is including the phpBB files it is starting at your document_root which might be pointing to your main website...
Other possible case is that when the Control Panel starts up it includes Joomla Admin files and verifies that an admin is logged in... so it might also be looking for administrator/index.php