Db Startup ERROR > ORA-03113: end-of-file on communication channel

SQL> startup

ORACLE instance started.

Total System Global Area 2147483648 bytes

Fixed Size 2926472 bytes

Variable Size 1224738936 bytes

Database Buffers 905969664 bytes

Redo Buffers 13848576 bytes

Database mounted.

ORA-03113: end-of-file on communication channel

Process ID: 4903

Session ID: 237 Serial number: 26032

SQL> alter database mount;
SQL> alter database clear unarchived logfile group 1;
SQL> alter database clear unarchived logfile group 2;
SQL> alter database clear unarchived logfile group 3;
SQL> shutdown immediate
SQL> startup