There are 2 things you can do:
1. Reload the dbms_debug packages.
As a result of previous dbms upgrades, the dbms_debug packages can cause problems. You can logon to the server computer, go to $ORACLE_HOME/rdbms/admin, start SQL*Plus under the SYS account, and run pbload.sql. This will reload the dbms_debug packages. Check if this has a positive influence on the problem.
2. Check for user trace files on the server.
If the Test Window hangs, it may be that the server process has died. Check if a trace file exist that is related to the problem, and if so, send it to me.