in my experience using plesk, it does not allow you to install in the root directory, try the following
go to control panel >> hosting >> web directories
add new virtual directory,
name > publicportaldnn
path > check
scriptsourceaccess > check
write permission > check
press “ok”
click “asp.net” button >> change version to “2.0.xxx >> press ok x2
go to hosting >> webdirectories >> publicportaldnn >> permissions
pleskiisuser >> full control
pleskiiswpuser >> ok
goto services >> databases >> add new database >> ok
add new user >> password etc.
open ftp client
upload dnn to publicportaldnn folder on server
initiate install by browsing to complete url. www.yourdomain.com/publicportaldnn/install/install.aspx
if it dont work try to turn on custom errors and try again
hosting >> web directories >> publicportaldnn >> asp.net >> custom error mode on “ok”
goto hosting log manager > click on log rotation > select by time weekly > switch on > click ok
now copy the entire dnn application to the root folder and you should be able to browse through the primary domain.
issues - ive had trouble setting up parent and child portals because of the why plesk handles dns
i dont use plesk anymore for dnn with mulyiple portals
hope it helps