The only thing I can suggest is to try enabling logging and see if the log shows anything clear:
Close Opera. Go to your Opera mail directory. Open accounts.ini in a text editor. Find the lines:
Incoming Log File=
Outgoing Log File=
And add a path/file name for the log files. Start Opera and try to connect. Which version of Opera are you using? As I haven't used Usenet for years I can't give you more help than that...