I shut my database down immediate
I changed my database from Archive mode to noarchive mode by commenting
these parameters:

#log_archive_start = true
#log_archive_dest = /11/oracle02/TESTDB/archive
#log_archive_duplex_dest = /oracle_direct/TESTD/archive
#log_archive_format = "arch%S.arc"

After I start the database as sys.

I later tried to connect using a username that has dba priveledges.
For 30 minutes, I could not connect. But If I connect as sys, no problem.
Has anyone ever experienced this problem? What's going on?