What is your OS?

IF it was on Unix, login as oracle user, then make sure
ORACLE_BASE
ORACLE_HOME=
ORACLE_SID=your_instance_name
LD_LIBRARY_PATH=

all had been set in your environment variable. You could check it through

$> env

if not set those environment variables and depending on the shell, you use export or setenv to set them.


Then

$> svrmgrl
$> connect internal
or
connect sys/passwd as sysdba
SVRMGR> startup mount
SVRMGR> recover database;
SVRMGR> alter database open;
SVRMGR> exit


Hope this would help you. IF you have any problems pl. let us know.

Sam