Has this database worked before ? If so, did you make any changes ?
There are more than one possible cause to this, such as incorrect SGA settings, ORACLE_SID or ORACLE_HOME not properly set, it could also happen when migrating the database…
Have a look at the following pages, hopefully you will find an answer there.
<a href=”http://arjudba.blogspot.com/2008/04/ora-01034-ora-27101-shared-memory-realm.html”>Oracle in World </a>
<a href=”http://www.dba-oracle.com/sf_ora_01034_oracle_not_available.htm”>ORA-01034: ORACLE not available tips</a>
<a href=”http://forums.oracle.com/forums/thread.jspa?messageID=1845760″>Thread: ORA-01034 & ORA-27101 at Oracle forums</a>