database not opening
Please provide further details about what happened previously. Did a hardware failure occur? Also, refer to the .trc files that generally follows ORA-00600 errors in alert.log. If you're on linux and made a default installation, alert log will probably be located at $ORACLE_BASE/diag/rdbms/sid/sid/trace. It contains the main DB events, and it's the first approach while diagnosing Oracle Failures.