I would make sure that 1.) all firewall/port considerations are opened from where you have dynatrace client running to the server. 2.) the server actually has two processes (frontend and backend) for the server. Make sure both processes are running. In the dynatrace server install directory > init.d, you will see the respective startup scripts that can assist here. The dynaTraceServer script will start both the frontend server and backend server processes.
Check out the documentation for further info - https://community.dynatrace.com/community/display/...
Oracle should be already present in external server.Create DB for the PW(say Dynatrace_PW)
In setting ->Dynatrace server -> Performance Warehouse -> Select "Oracle" as DBMS -> Database name as "Dynatrace_PW" -> username and password for Oracle Login(has access of read/write permission to the database -> DB port as "1521(default oracle port)" -> click on "Test Connection".
Be make sure that port 1521 be opened between dynatrace server and External server(where oracle is installed)
Hope this may help!!