>> Are you sure your firebird is actually running?
>
> Yes!... Like I said I can connect via isql...

Note, when you use

CONNECT '/home/myhome/mydb.fdb' USER 'sysdba' PASSWORD 'masterkey';

isql uses IPC to connect to your database. To be sure that your TCP/IP stack
works correctly, use

CONNECT 'localhost:/home/myhome/mydb.fdb' USER 'sysdba' PASSWORD
'masterkey';

Roman