DB is hanging

Hi All,
I have a problem with my database. When I try to connect to my database with SQLPLUS:

SQL>sqlplus / as sysdba
SQL>connected
SQL>Select * from tab;

I get the following error:

ERROR at line 1:
ORA-01012: not logged on

If I try to connect to my database with /nolog:

SQL>sqlplus /nolog
SQL>conn sys@orcl as sysdba

Connected to an idle instance.

I cannot shutdown my database.

I have checked the alert.log having entries like below:

Sat Feb 16 06:00:32 2013

Process m000 died, see its trace file

Sat Feb 16 06:00:32 2013

ksvcreate: Process(m000) creation failed

Sat Feb 16 06:01:35 2013

Process m001 died, see its trace file