If all tables registered with ArcSDE have been dropped *AND* there are no
tables using ST_GEOMETRY in the instance, then the easiest way to fix your
ArcSDE instance is to "DROP USER sde CASCADE" and reinstall.
Note that if you *DO* have outstanding tables with ST_GEOMETRY columns,
then dropping SDE will corrupt your Oracle instance to the point that it too will
need to be dropped and recreated.
If you are uncomfortable doing SQL queries against the SDE metadata tables
to assess the status of your instance, then you should probably log an incident
and have a Tech Support analyst walk you through the necessary steps.
- V