If you are trying to change the character set, do the following:
% svrmgrl
SVRMGR> connect internal
SVRMGR> shutdown immediate
SVRMGR> startup mount
SVRMGR> alter system enable restricted session;
SVRMGR> alter system set job_queue_processes=0;
SVRMGR> alter system set aq_tm_processes=0;
SVRMGR> alter database open;
SVRMGR> alter database character set WE8ISO8859P1;
SVRMGR> alter database national character set WE8ISO8859P1;
SVRMGR> shutdown immediate;
SVRMGR> startup restrict;
SVRMGR> shutdown immediate;
SVRMGR> startup
SVRMGR> shutdown immediate;
SVRMGR> startup

This procedure is outlined in http://metalink.oracle.com/metalink/...T&p_id=66320.1 and explains why the database has to be shutdown/startup so many times.